DK,
Seat and crimp in two separate operations. Use the bullet seating die to seat your bullets to the top of the cannelure/crimp grove (so you can barely see the top of the cannelure/crimp grove).
Assuming you are using Hornady dies, the TC die is a combination taper crimp and roll crimp die. With a seated bullet in the shell holder, and the press handle all the way down (ram/seated bullet in shell holder all the way up), screw the die into the press until it stops. Continue screwing the die in until you see a definite roll crimp in the cannelure/crimp grove. You will feel resistence before you obtain a roll crimp -- this is the taper crimp section of the die doing its work. You may also have to move the handle up (loaded round down, away from die) in order to continue screwing the die into the press. Do this a little bit at a time (half a turn at a time at first, then less as necessary) to get the crimp you want. If you get to a point where you really have to force the handle, stop and back the die off a bit (otherwise, you may buckle the case). Just go slow the first time, and you'll get the hang of it.
Paul