tranny seal

anybody got any tips on putting in a tranny seal.. I've put them in before and not had problems but i just screwed one up trying to get it in... I usually use a ratchet end and extension thats the same size as the seal and then i crawl under, set it in place and tap it in.. this time it went in but it's leaking because it didn't go in perfect (the sides of it got all ripped up.. sorry about the long post, any tips would help. Thanx