What we really need is a directory of instances by theme/focus, not just by level of rules enforcement.
My most important advice is start on a smaller instance, follow lots of people, and don't be afraid to butt in on conversations as long as your goal is not to be offensive. And if you're accidentally offensive and apologize sincerely, people will forgive you and life will go on.
@DialMforMara That would be nice.
Related research (only currently open registration though):
Please, use it if you find it helpful (I'll try to update it when new instances go up).
If you create such a website, please, let me know :)