Between Scott Kelby and John Beardsworth, these two lists of Lightroom tips provide lots of useful pointers:

• 10 Things I Would Tell New Lightroom Users (Kelby)
• 10 Things I Wish I Could Tell A Slightly Less New Lightroom User (Beardsworth)

Kelby’s tip about “solo mode” is pure gold. I’ve been using it for a while now and it’s a super way to work. I’m not sure about the keywords tips, though: Both Scott and John caution against keywords and nesting keywords; while I agree that finding a way to use consistently use keywords (and metadata in general) is important, I haven’t run into problems of too many of them, quite yet. Periodically taking a keyword inventory and identifying duplicates has helped keep my catalog relatively clean (and me relatively sane).