I have not tried to estimate my plays if they are +EV, and I'm not sure if I want to try either, ref
this article about +EV. Even though I make my predictions, how can I find out whether the numbers are correct or not? Have you tried it?
My bets are based on as much information I can gather about the game; statistics, form, previews, injuries/suspensions, transfers, trends, historical data, weather, upcoming events that can affect the match etc... The same information as most of the other tipsters are looking for, I guess. But I always try to improve, so if you have another approach I would love to hear more from you.
Good luck!