Now that I've conquered the trim in 3 rooms, can I consider myself an expert? I've learned a lot along the way and I wanted to share my tips.
First off, be SURE you want to do this. You can't go back!
Once you're sure, start by lightly dusting the trim with a rag. People may tell you to lightly sand, but I've found that it really didn't help at all, so don't waste your time.
Paint on your first coat of primer. It should be pretty thick, but not horribly thick that it dries weird. After trying a couple different brands of primer, I prefer Kilz.
Primer dries pretty fast, so you won't have to wait too long to do the next coat. Again, add a thick coat, but not too thicker. The thicker and neater you can get it on, the less coats you'll need.
And as you start to get sick of doing this, add one more coat of primer. The wood grain should be showing less and less after each coat. I promise you're getting closer!
When the wall color is done, continue with the trim. I switch over to a semi-gloss white for the final coat or two. I like semi-gloss for the trim for a brighter finish.
That was a LOT of work and I promise I never could get this done in a weekend. All 3 rooms I've done took weeks or months to finish. Anyone wanna come do the rest of my house?
I'm linking this tutorial up here