Traffic is the more negative side of Bali. If you are stucked in traffic you can spend easily and hour on a few miles moving only very slowly.
Knowing you will not be able to avoid it fully but here are some tips.
1) Choose Location and Attractions wisely before you book:
Book a hotel which is outside of the heavy traffic zone and from where you can access main attractions without passing traffic zones.
For example: If you book a hotel in Jimbaran (which is on the south tip of the island) and you plan to spend most of your activities around Siminyak, Kuta, Ubud or Canggu than you need to pass trough a narrow, heavily congested area around the neck of the airport. Its better than to spend your holiday on the south tip and travel out maximum to Nusa Dua or Sanur. The same if you stay in Nusa Dua or Sanur.
On the other end if you book a hotel in Canggu, Pererenan you will he mostly outside of the tourist zone. You can easily access Canggu, Pererenan, Tanah Lot, Ubud without hitting massive traffic. You can also head toward Seminyak but expect some traffic on your way.
2) Avoid rush hours:
In the morning between 8-9 am when staff drives to work and evening 5-7 pm when people leave work is not the best time to be on the road towards traffic area.
3) Choose Sundays:
Sundays roads are less traveled than on other days of the week.
4) Choose scooter over car:
Cars move very slow in traffic, with a scooter you can slip trough the cracks and be much faster. If you don't drive your own scooter you might opt for a Go-jeck scooter instead before taking your own car or a taxi.