It’s easy to limit ourselves to obvious selectors and then get completely crazy with id and classes - and the way I do it it’s not efficient at all and nearly as tedious as inline style.
This might help: 30 CSS selectors to know.
Again, this is from Colt Steele - The Web Developer Bootcamp (I’m not pushing anyone to spend money to learn at all, just giving credit).
[EDIT]: I realise there’s already a very nice Wiki article here, so sorry for the duplicate.
Here’s a CSS cheatsheet on CSS selectors !
A nice way to discover new “tricks” is to check out this thread.
To have some understanding of what selector > selector means, check out this thread.