The best way to do that is to decide what you are going to call the "top" of the list for your upvote. Will you call the limit at a dollar amount or a certain number of upvotes already? I prefer to throw my money in on early stuff. If it is on the trending page already I will usually reserve an upvote unless I really like it. For the most part, I comment on the trending page stuff more than I upvote and upvote more on the lower valued stuff from smaller accounts.