Hi i was wondering what the guideline is for creeping the different levels of camps.

I'm playing lost temple a lot and I just creep the middle (not including the fountain) until i get my 2nd hero then go do all the shops (orange level) then i attack.

I never really bother with the red creeps. should i?
I assume the goal is leveling more than getting items. true?
Also i dont creep the camps where i think my units will mostly end up in the orange health since i have a bad habit of my opponent sneaking up on me then killing me when im weak. Should i be pushing that hard on creeps so that im quite hurt by the end?