The first thing to do is determine if you are carrying the correct total amount of weight. A good way to do that is to check at the end of a dive, in shallow water. If you can exhale and lie on the bottom in four feet of water with 500 psi, then you have enough weight; you can try taking some off and see at what point you can't stay down any more. That tells you how much you actually need.
Once you have determined that, you want to distribute the weight so that you can hover horizontal in the water without having to move your legs or arms to keep your position. That's easy to figure out -- just stop moving, and see what happens. If you slowly tilt feet down, you need to move some weight up, onto your tank or into your trim pockets in the back. If you tilt head down, you need to put more weight in the lower, front pockets or on a belt.
You don't distribute your weight to correct your position on the surface. Getting your head pushed forward often means that you have overinflated your BC, which may indicate that you are carrying more weight than you need. You are right, though, that having a lot of weight in front weight pockets and all your lift behind you WILL increase the tendency to pitch forward on the surface. If the BC isn't overinflated, that's generally pretty easy to compensate for just by leaning backwards.
