Mostly you want to max your Q for maximum damage output, but if you are having a hard time with harass maybe max your W to counter that. Your R is a great gap closer, but try and land cresent strike before you jump to save CD time if you can.

Your combo is gonna be W-Q-R-E-Q-R

Throw your shield up
shoot your Q
jump on em
get some passive pops in
Bring them back with your E
shoot your Q again
Jump on em again
There either dead, almost dead, or you should run.

(Q)Cresent Strike:

This is gonna be your main poke/damage spell. If your following this build, your gonna want to use this for mostly poking, and to let you use your ulti twice. Rely on your passive and basic attacks as much as you can.

(W)Pale Cascade:

Your damage pillow. This can be really helpful if you use it right. When fighting, try to position yourself so that your bubbles will pop and you get your double shield. activate it after you jump on champs rather then before so you get longer spell time. Throw it up if lets say pokes with his spikes and you can't dodge it, or if rolls that annoying dirt circle at you. You get the picture. Also good for clearing minions.

(E)Moonfall:

This is a pretty annoying spell to go up against. Enemy team: "Look I can get away! oh wait... Diana killed me."
When your enemy thinks he can get away, bring him back and get as many passive pops as you can before you can jump on him again.

(R)Lunar Rush:

HUGE gap clearer. Won't do as much damage as a regular built Diana, but it does the job. If you can hit your opponent with your Q before jumping, you can get instant CD, but if you need to catch someone you just want to go for it, that works too. If your being chased and you happen to be next to a jungle camp, shoot your Q over the wall so you have vision and jump on the jungle minion with your ultimate. Works for every jungle camp. Careful being the one to engage the team fights: If you are at the point where you have plenty of health, be my guest. otherwise I highly suggest picking off the carries or targets.