What should I prepare for going to Bali in April?

It's quite hot in June, April and June. Remember to bring more short sleeves and so on.

Also, it may be cold at night. Take a thin coat and an umbrella with you when you leave. Do a good job in mosquito prevention and heatstroke prevention. There are mosquitoes, but not many. You should eat seafood there and take some antidiarrheal drugs.

Passport first, then visa.