There are two basic ways to approach sports betting with skill.

Top down betting
Also known as "Steam Chasing". Finding the leading sportsbooks where very smart bettors bet and that move the market.
Betting at a sportsbook that is slow enough to change the odds and getting the odds before they move there. This also includes arbitrage, you basicly do the same thing as the arbitrage window is closed quickly.

Bottom up betting
Also known as "Originating" this means making your own odds using some kind of model based on data that you have collected. Then you compare the odds that you have created to the bookmakers odds and finding places where you get better odds than your model. This can also include elements of qualitive data which means watching teams, knowing about sithuations ect.