This isn't a cheat, really, but I found it humorous. When you start a new game, WALK everywhere in Garden. It takes a little longer to get everywhere, but you're "Conduct Points" on your SeeD Test scoring go up (helping to bring up your rank!).

BTW, if you're bored, go to the classroom an @nd floor, and turn on Squall's desk. Read some of the things. Very funny! The Sorceress' Knight? No animals alowed in Garden? What? Who's J.I.? Poor Seifer.