You have two options (that I know of):
1. The military tuck. You start on one side, just at the front of the hip, and take the extra material and fold it over towards your rear. Holding that side in place you repeat on the opposite side and then carefully button your pants without disturbing your neat and tidy folds. With practice this is rather simple, and looks nice from the front and back (though a little out of place from the side, particularly if you raise your arms as the fold is larger at the waist than at the armpit).
2. You give your tailor $7-12 and have them alter the shirt.