Also, make sure you understand why things happen the way they do. If there's an issue with the layout and you manage to fix this by trying some different things

Also, make sure you understand why things happen the way they do. If there's an issue with the layout and you manage to fix this by trying some different things, take the time to figure out why the fix worked--things like the box model, collapsing margins and containing floats are all worth understanding. Your designs will feel less like a fragile house of cards, too...