Check what a bet is worth given your odds and your win probability.
Expected value is the long-run average of a bet: (win probability x profit) minus (loss probability x stake). Positive EV means the price is better than your estimate of the true chance; negative EV means the price is worse.
The hard part is the win probability. A useful starting point is the no-vig fair probability from the market, then adjust from there if you think you know something the market does not.
Strip the juice from any two-way line and see the fair price.
Combine up to eight legs and see the true payout and implied odds.
See how much margin the book has baked into a market.
Work out the hedge stake that locks in the same profit either way.
Size a bet from your edge and bankroll with the Kelly formula.
See what a bonus or free play is really worth after the rollover.