Most of the time you're completely reliant on your E and W to fight. If you miss both of those on most enemies, you're not going to be winning the fight. Always remember how much movement speed you can get from your Q as well, it can be a life saver at times. Your ult should only ever be used at the start of a fight, to dodge a skillshot, or to catch someone trying to run away. A good example of this would be against an Ahri. You can either ult her at the start of the fight so that she has to fight you, use it to dodge her E so that she has no more CC, or use it when she tries to escape (typically with her ult). TL;DR, Q for speed and damage, W for heal and slow, E for dash, stun, and attack speed, and R for catch or dodge.