Does anyone have advice for getting to 3 star rating

Some basics...Clean your island every day. Pick up weeds, branches, etc. Actively work to gain materials and build items for decorating, etc. Buy/plant flowers from Nook's Cranny and Leif.

Don't leave random items laying around the island. If you don't have enough storage, find somewhere to drop it in your house, don't leave it out in the open. Talk to your villagers and visitors regularly.

i have a 3 star rating all you need to do is put stuff down on your island

Listen to Isabelle. She'll give you tips to improve. You need to have enough villagers too. Google can tell you how many.

Yes, and spread out your decorations around your island too.