I suggest you read my other guide about Fantasy Tennis, the feature guide before moving on to this one. Anyway, let us begin. In the game, currently, you are able to use only 2 quickslots. So buy 2 quickslots, and then equip them to your character. I suggest fireball and meteor. Also note, quickslots can ONLY be used in battle mode. Choose wisely, since quickslots cost a lot, unless you want to find them at Guardian mode or by fulfilling the recipe requirements... Just get those quickslots.
Why fireball and meteor? Well, fireball, because, as soon as your guardian or you hit the ball, you are able to push your opponent away and immobilize him for a few seconds, which can render him unable to get to the ball. Why meteors? Serious damage when they hit, and they also immobilize your opponent a little, but it`s pretty hard to hit him with meteors, unless you`re a super lucky person or something... Alright, now, you should choose a suitable playing mode for you. If it?s a double match, you have these playing modes: Front & Back, and Sides.