Overview: The airport is in Denpasar - not much here though except the only airport in Bali. Close by are Seminyak and Canggu (west coast = surfing side, higher waves, darker sand, the majority of expats live here so lots of western restaurants/bars/cafes, around 1 hr drive from airport), and also closeby are Sanur and Nusa Dua (east coast = snorkelling side, lighter sand, but if you're wanting incredible snorkelling then head to the Gili islands or Nusa Lembongan). Ubud is closer to the centre of the country (yoga place, monkey forest, cycle through rice paddies, Bali swing, coffee tasting, waterfalls, hike to the top of Mount Batur in time for sunrise here but you can arrange that tour from most places in Bali), Uluwatu on the southern tip for beautiful sunsets and you can organise to see a Kecak Dance (Balinese dance) but there are very few restaurants/cafes in Uluwatu so you need taxis to get around really as it's not very built up, Gili Islands off the southeast coast (only been to Gili T which is absolutely beautiful, clear water, huge turtles when snorkelling/diving, boat trips, BUT when Bali becomes more available for tourism again, it is known as "the party island" so best to avoid if many tourists are around and head to Gili Meno or Gili Air instead where it's quieter).
More detail of the above:
On the west coast is more surfing places, higher waves, darker sand on beaches but it's full of expat westerners and nice bars :) google or Instagram search Seminyak and Canggu to see what it's like there. Lots of surf schools along the beach to learn or rent boards from. Our favourite places are Seminyak (slightly more touristy) and Canggu (slightly more expat-y) which have a stunning sunset every night (as does everywhere along the west coast) and is only a short taxi between Seminyak and Canggu. Other than surfing, bars and coworking cafes in Canggu, you'll have to get a 1-2 hour taxi to one of the snorkelling (Sanur) or monkey places (Ubud). Seminyak has cute shops, bars, restaurants, massage places (but to be fair everywhere in bali has all of these things!) If you want a beach sunset evening - head to any one of the bars on the beach like La Plancha with bean bags on Double Six beach. Or reserve a table at Moonlite on Double Six beach which is 3 floors up and is based on a glass balcony where you'll have cocktails and dinner if you fancy. Sunset is 6.15ish so get your table for 5.30pm reserved at the very front of Moonlite. At 9.30pm, Motel Mexicola stops serving food and everyone dances on the tables because they're screwed to the ground. Either stay there for your night or walk down the road to La Favela for another club but this one is open air and has 2 or 3 floors (I can never remember 😂). If you want another bar along the way, Rumours is opposite La Favela :)
On the east coast e.g. Sanur and Nusa Dua, is whiter sand (still not snow white like the Gilis) and better snorkelling (I can't actually verify that as the day we wanted to go snorkelling we had our moped crash when we arrived so I didn't actually get a chance to try it out but rumour has it snorkelling in Sanur is good). There is no view of the sunset over the sea on the east side of the island so head to Canggu/Seminyak if you want this. The key difference between Sanur vs Canngu/Seminyak is that Sanur has much whiter, finer sand, swimming and is more quiet, whereas Canggu/Seminyak has darker sand, is busier, touristy, excellent sunsets, surfing.
If you want a black sand beach almost all to yourself, head to Seseh Beach (a short drive from Canggu) for around 6am in the morning where there'll only be the odd dog walker. No sunrise of course, since this is the west side of the island where you can only see the sunset, and high waves but the peace here is beautiful in the morning. There are no restaurants/cafés on the beach so it's very isolated, perhaps keep your taxi waiting for you or prepare to wait up to 15mins usually for an online taxi to arrive, but an hour or so here in the morning is very refreshing.
Uluwatu is on the most southern tip of Bali and has incredible cliffs with views of the sunset, you can take day trips here, it's not as built up with restaurants here but when we stayed here it was so peaceful and stunning, we also visited the Balinese Kecak Dance they do here which is a part of their culture where they put on a theatre show with no speaking in front of the sunset in an incredible amphitheatre. You probably have to book in advance! And pre arrange transport back to your hotel after the sunset kecak dance because we didn't and everyone left and we were the only people in the car park, no taxis anywhere, monkeys literally surrounding us and trying to take our flip flops and bags 😂 We tend to stay in the Renaissance hotel here when we visit (in the Marriott hotels chain) which is beautiful - see their IG!)
When you are in Ubud, (just over an hour drive from Seminyak/Canggu), this has a laid back vibe, lots of people in yoga pants, lots of yoga studios and meditation sessions, the Pyramids of Chi are here where you can get sound healing through gongs and beautiful instruments while lying in a pyramid, rice paddies everywere, check out the monkey forest in Ubud and also here are tours to the waterfalls, those classic Bali swings, rice terraces, coffee tasting etc usually all done in one tour on one day. The best road to have accommodation near to is Monkey Forest Road - this is the central road with access to most restaurants, tour operators, yoga places, and it's a short walk to "Yoga Barn" so we always plan our accommodation around or on this road. Also on this road is the massive market for souvenirs/clothes/accessories is at the top of the hill (opposite end of the road to the actual monkey forest).
Ubud has no sea view as it's a rice terrace vibe so the only thing I miss when I'm here is watching the sun set over the sea at the beach. Veryyy few bars here compared to the coast as it's chill here.
While you're in Ubud, check out a little restaurant called Bale Udang which is a short drive from central Ubud (Google it, it is stunning and you can buy fish food to feed the carp fish - the restaurant is essentially made up of multiple "Bales" (floating sheds with tables in the middle to eat at) that surround a sort of pond filled with coy carp fish, you can negotiate with the driver to wait for you for around 2 hours while you're there since not many taxis drive around there. Tebasari Resto is also a beauuutiful place to head to when in Ubud. I did this beautiful cycling tour through the rice paddies (90% downhill so very easy, plus you can opt to walk your bike up the 2 steep (short) hills which most people do!) which combines looking around Balinese houses and coffee tasting too: https://www.airbnb.com/experiences/187474
Gili Islands/Lembongan: (We planned to go but had a moped crash in Sanur before we left for the Gilis so couldn't go in the end so sorry I can only say most of this from friends' experiences) There are 3 Gili islands, I've heard that Gili T is more party-ish, Gili M and Gili Air are more honeymoon-y. All have incredible clear sea and white sand (see Instagram), boat trips, snorkelling, scuba etc. You can only either cycle around them or hire a horse and cart because cars don't fit on the narrow streets of these small islands. At the moment you need a covid test to go there as it's by boat but not sure what the rule will be later this year. If you want the idyllic white sands these are the places to go. Lembongan is a much shorter boat ride from Bali and is considered part of Bali so at the moment (Aug 2021), you don't need Covid tests to get on the boat.
Taxis only really accept cash (if you're using the uber-esque apps then to pay without cash means topping up your account in a supermarket) so ideally get some cash changed at the airport or before you come for that first taxi at least. There's tonnes of currency exchanges around bali if you need them but you always need to bring your passport to change cash. Download the apps called "Go Jek" and "Grab" which are Bali's version of uber (uber got banned a couple of years back), you can order motorbike taxis or car taxis through them - the only issue is when you're at the airport it can be a bit confusing trying to find the grab/gojek pick up area as you lose wifi as you're walking from arrivals to there, so best advice is probably to take a local taxi (ideally a brand called "BlueBird" as they're known around Bali and aren't likely to rip you off) for your very first drive from the airport to hotel and then sort out your Grab/Go Jek apps.
Taxis - do notttttt take local taxis off the street with no signage on them. They have what we call the "taxi mafias" in some places and I've heard of awful things happening sometimes when people take them. Only get Bluebird taxis off the street or Go Jek or Grab taxis from the apps. If you want to take a motorbike taxi from those companies, you have to insist they give you a helmet because there are police stationed at random points who always pull over people with no helmets and ask them to either pay a bribe or go to court. Your first taxi from the airport to Seminyak should be 250k - 300k I'd say :) I'd highly recommend not hiring a motorbike unless you have a license in your home country; almost everyone hires a bike but I haven't met one person who hasn't had a crash of varying degrees of severity. Hiring online taxis and online motorbike taxis are far far far safer.
SIM card - go for Telkomsel, for reference I pay 139,000 IDR (£6.80) for a month's package and get 30GB & 300mins which is more than enough. You can buy a sim at one of the stands at the airport or lots of places in Canggu/Seminyak, I used to pay 100k for a sim and then top it up via the MyTelkomsel app if needed.
Drugs - death sentence for this so keep away from anyone you think might be on them! I've heard that some dealers set people up by selling it to you then telling the police you have some and then halving the bribe you're asked to pay to the police.
Money exchange - ideally get this done before for ease :) if you get it done at the many in Seminyak then they all say no commission but very few will cheekily take some out sometimes so always double check their counting at the desk no matter how long it takes (my friend was tricked out of 2million last month); if they try charging you more just ask for your money back and say you'll go to the one next door as there's so many of these places.
Beach bars/sunset bars:
Seminyak - Ku De Ta, Potato Head, The W,
Canggu - La Brisa, The Lawn, Finns Beach Club,
Uluwatu - Omnia (more of a night club with pools, or day pool parties), Rock Bar 👍
In terms of the vibe you're looking for:
More cultural / serene = Ubud (but there's no beach here)
More vibrant with other tourists and beaches = Seminyak / Canggu
Snorkelling / Serenity / White beaches / Crystal water = Gili Meno or Gili Air