- Create a permissive ruleset. Say "Yes you can, and here's how!" instead of "Not unless you took the feat last level!"
- Focus on playing the game, not the rules. Building the most optimal character you can shouldn't matter. What should matter is how much fun you derive from playing.
- Magic comes from the character, not from his/her Christmas tree of items. (Magic means two different things in that sentence, in case it wasn't clear.)
There's a decent enough description of "old school" that can be found here; I won't fully embrace all of those ideas.
I'll see if I can't get the core rules I have typed up and posted by tomorrow.
There's probably going to be a lot of my "design process" (if you can call it that) showing through; this is by no means a finished product.