If you haven't checked their ban on non-essential goods, then it's the first to read.
Then - niche research. I use Helium10 for this, it's the only tool you will need. I used JS, VL and some others, but they are worse.
From my experience, product research is the key. But learn from my mistakes - always test with small batch on FBA and consider it when you do niche research.
And don't wait for high margins, they are much lower now than a few years ago.
If you don't have 5+ k $ to invest, there are better niches to work in