My 2cents:
Basketball (NBA and NCAAB) are the most difficult games to cap, NBA in particular. The bookmakers' lines are usually very sharp to start with.
Baseball is where the money's at.
I can suggest a very simplified way (this being a newbie forum, I hope you don't treat this as condescending). Pardon me if this is "too obviously clear" for you.
The key is identifying value in the line. Let's say a book offers odds on coin flip; -105 heads and -105 tails. There's no value here because ultimately in the long run you'll get 50/50 distribution on heads and tails and you end up losing out on the vig.
However imagine a scenario whereby a stupid book offers -120 heads and +220 tails. If you pound tails all the time eventually you'll come out ahead.
So similarly, you need to cap the chances of winning of a game :lol: easier said than done I know...