In order, and quickly, I look at the abstract, the picture at the top of page 2 (unless it was on page 1 like vision and graphics papers tend to do), the references, the conclusion, the lit review, if I’m still interested I try to scan the whole thing to decide what the main point of the paper is. Then if I care to, I start again and read it linearly start to finish.

If I’d agreed to review a paper, I don’t get to abort the process. Otherwise I can bail at any step.