O1-O2-R1-R2 is possible, but that is not the rule. The correct order (if this is the only rule) could be O1-R1-R2-O2. If you wrote down O1-O2-R1-R2, you could miss a possible correct answer.
If I'm stuck on a game I come back to it last. Usually I find I just don't know how to set-up my diagram, so if I'm in that situation I look at the grab-a-rule question first to help me out :) Good luck!
Yep. I go through each indented rule methodically and piecemeal. Afterwards, you can step back and see how the rules interact with one another (because they always will) and see the relationship in a holistic way.