I remember reading a few Steem posts on the ins-and-outs of curation rewards .. honestly, the timing when getting upvotes seems to be quite complex ... but if I come across something I enjoy reading, I usually will upvote anywhere from 75 to 100%. I also don't hesitate to down-vote crap content (lately, there's a bit less of the spammy comments and such, which is good - glad the Steem Cleaners are out and about).