Props are by FAR one of the easiest ways to make money, as long as it is not in the "tried and tested one" or "coin-flip" category.
Who will score first? This falls into the tried and tested category. Give an accurate spread and no special knowledge, this prop is tough to beat. But if you know that one team always kicks, while the other receives, this prop is beatable. Or, if the prop is left open until after you know which team is receiving, you can have 10%+ EV.
Margin of victory props... these are also "tried and tested" - and never have value.
Player statistic props are often beatable using a straight poisson distribution. If you gamble and don't know what that is, learn! 80% of all props can be analyzed using that, and fully 1/4 of Olympic's opening props have value - they typically open at -115 and let the market bangit into shape.
Realize, a football line reflects 20 different opinions. It might not be perfect, but it will usually be pretty close. A unique prop offering though, is one opinion. That is why there is often so much value.