When you play sion its very importent to learn how to last hit minions which is also why i take Enrage lvl 1 so that i get some bonus exp already from the start

In team fights remember to use ulti because the ulti heal all your teammates, and you will rest longer in team fights, but be careful and let the official "tank" go first.

If you chose frozen mallet instead of warmogs then do not take exaust but rather some heal or fortify.