Upvoting is also a great way to promote yourself! I tell you how I work.
If I read a post I like I give an upvote same for comments. If I can't I forward it to my blog and try to do so later.
I work through my notifications and comments and upvote good comments (it turns out to be lower than when I give to a post but in my opinion, good comments should be rewarded).
Another time I check those who upvoted me and I upvote one of their posts. It depends on which one... but in most cases if I do not see an eyecatcher I take the one that is 6 days old (or even 7 and still a few hours till payout).