You could probably check out
There are levelling guides for most classes… Most are still a little outdated (ie. not 0.83 yet) but the general ideas should still help you…
Generally tho, you shouldnt really be struggling in the campaign stages (at least till Act 8 & 9) even if you havent grasped the class concepts yet… The key thing is to play to the skills you want to use and check the alt information for what attributes affect the skills the most… and just generally dont forget things keeping resistances in line with your level and stack a little health/damage mitigation here or there if you begin to feel a little squishy…