For fit, you can get your measurements at a tailor if you don't want to take them yourself.

Fashion style is very personal. I've found that you'll need to do lots of observing and "stealing" what speaks to you. I get my styles from people-watching, following /r/malefashionadvice and doing more research on clothes I saw someone wear in a tv show!

That said, fit is absolutely the most important factor and is what people look at first when they notice you (IMO)

For about 15 years trial and error, then I started wearing just black, and 6 months ago I started watching YT videos on the matter. I prefer a British youtuber called Harry Has. I have watched some of his vids during lunch and slowly gained some intuition.