Corners are where races are won and lost, period. It is good to see your more worried about corners more than jumps
. Anyways, they do take a while to really figure out. We could sit here and tell you step by step, or you could read a how to on a site. Truth be told, however, nothing we can do will have as much of an impact as you getting out there, experimenting, and getting more comfortable on the bike on the track.
That being said, there are many different ways to tackle corners. They all vary for muddy, sandy, dry/hardpacked, flat (no berm), bermed, loose dirt on top, slick, etc.
A basic way I tackle corners is to down shift before you are into the turn. Then you aren't trying to do too many things at once. I have been experimenting with standing up going into the corner, sitting down at the apex (actually angle part of it) and stay sitting or stand up (depending on conditions, jumps, etc) coming out of the corner. It helps tremendously, however, it can feel a little scary at first because you have less surface area on the bike, therefore less control. However, it is the proper way to do it.
As for clutch and throttle control, you should go in with a steady throttle and ALWAYS keep a finger or two on the clutch, ready to use it if you get squirley or anything. In fact, on a 125, you have to use the clutch in all corners, just because of the way the power is delivered. You should use it on a four stroke too. The only time I can think you might not need to use it is on a very, very wide, sweeping turn. Even then, you should have your fingers on the clutch.
Things to remember:
1) Look ahead, not at your front fender. You will go where you look, and your body will handle not hitting the huge rock with out you looking at it (as long as you saw it..))
2) FINGER(S) ON THE CLUTCH AT ALL TIMES!
3) Balls of your feet on pegs. The foot pegs are the lowest part on the bike, so you don't want to get your knee or hip screwed up by having your foot ripped off.
4) Elbows up, like your doing a push up on the bars, to maintain maximum control.
5)Stay loose and try to flow. With more experience you will be more assertive, and it will be amazing how far you can push the bike around a corner before you fall if you carry enough speed.
6) The throttle is your friend. If you get in a tight situation, gas it (Even if you fall, its better than falling over cause you were stopped, right? )
7) You need to be as far forward on the bike as you can. Almost like you are sitting on the gas tank. Watch the pros, its how they ride and its how you are supposed to.
A finger on the front brake, and be prepared to pres the rear brake as well.
9) Remember, stand on the way in if the space before the turn is rough or choppy. Sit down after the apex, or stay seated throughout the turn if it is smooth.
10) Roll on the throttle and let out the clutch to optimize power.
Edit: Wow, I was typing all that and hadn't seen Nick's post yet, so I'm sorry Nick; I basically said some of the same things you did without realizing it.
Great minds think alike
. I forgot about the weighing the outside peg and the pressure on the front brake is new to me. Cool!