Actually, it's two different things.

"Lean" refers to the needle valve setting. If it's turned in (clockwise) too far, the engine doesn't get the proper air/fuel mixture (to little fuel for the volume of air is lean).

Turning the high speed needle valve counter-clockwise will richen it a bit. Problem is, you don't really know if it's too lean without running it. (Or trying to.)

If the engine is much too lean (or rich), sometimes it won't start. Good rule of thumb is to turn it all the way in, then back it out about 2 1/2 turns to begin with. It should start, adjust it from there. By the way, just turn it "in" until it bottoms out, don't close it too tight or you can screw up the needle valve.

There's so much more to tuning these things that we can't put it all here (or at least I can't ). So it's best to get someone's help. Your instructor's the best bet.
Dennis-