The best way is to turn the rack all the way in one direction. then turn it all the way to the other direction and coun't the number of turns you get out of the wheel. If you get 4 turns lets say then if you turn the wheel full to the left and count 2 turns to the right when the wheel reaches 2 turns the rack is centered or at least close to where it can be adjusted with an alignment.

But the problem is this. If you didn't have the rack in the same exact place when you hooked the rack back up the cable reel may be turned a revolution or 2 more in on direction than it should be.

Basically the best thing to do is try centering the rack like i said. then remove the steering wheel and look at the attatchment about seeing if the reel is aligned in the center. If its not remove the universal joint on the end of the column that attaches it to the rack and move the column untill the marks line up then reinstall the column.