If you want to learn new enemy skills, its best to first manipulate the creature you want to learn from. creatures like zemzelet never uses white wind, so you have to manipulate it in order to learn it. Also look for the enemy skill "Aqualung from Jenova Life in the City Of The Ancients. Its Very powerfull. Also, When You've just left Midgar, look for the custom Sweeper to learn Matra Magic. It's very usefull if you plan to level up later in the mythril Mines. And another: The Materia keeper in Mt. Nibbelheim uses "Trine" Enemy skill. Don't miss it.