If your cookies are too hard . . . They may have been baked too long or at a temperature that was too low. Too much flour or not enough shortening or liquid will make them hard also.

If your cookies are too tough . . . You may have used too much flour. Unless you want a chewy cookie, do not use bread flour. Check your measurements--the cookies may not have enough fat or the amount of sugar may be wrong.

If your cookies spread too much . . . The baking temperature may be too low. Too much sugar or shortening will cause spread. If pans are greased with too much shortening, spread may occur. Add a little more flour or chill your dough before forming the cookies.

If your cookies are too brown . . . You burned them! You may have cooked them too long or at a temperature that was too high. Too much sugar may also do it.

Two great articles, and where I got a few of my tips, are available at Good Housekeeping and The Prepared Pantry.