I'm still learning the ropes and would hate to give you wrong information on how the whole system of upvoting works but I'd genuinely say upvote for content you think is really good and comments you agree with on posts because each upvote is worth a certain amount so use your upvotes carefully. Here is a little article on upvoting though - https://steemit.com/steemit/@averagejoe/what-i-ve-learnt-about-upvoting-on-steemit-the-10-commandments-of-upvoting :)