Sheik....
I recomend you to be very, very fast and accurate in all your attacks. And when you go offensive, let your attacks flow like a river. Grab alot so you can have possibilities of starting combos and chain grabs[not all players can be chain grabed well].
If your opponent is playing "defensive" use the Side A which does the double kick to break his defense, or the Down A to do the brake dance.
I recomend you to learn 'tech' and 'wavedash' to reach a good level. Use the Ground Dodge ( L or R Down ) to evade fast attacks received.
'Needle Storm', always apply it to battle, because it can be very helpful in a intense battle.
To cancel it, press L, R , or Z.