What I know to be successful is you should do the follow ;
1- manage your bankroll properly, and start with a decent bankroll, you aren't playing, you are investing for your future.
2- be discipline all the time.
3-master the game you are playing in sports, at least focus on one league so it's easy for you to master it.
I’m not sure if it’s just me, but your no 1 makes it sound as if you’re treating gambling purely as a means to earn money purely – having that mindset is not always good.
The remaining two are very good, they’ll increase the possibility of you getting more profits than losses but the profits is still not guaranteed (remember you’re dealing with gambling). But as for the number one, no body should take it as a form of investment, its important for you to know how to manage your bankroll properly, know when to call it a quit, know when to make withdrawals, know the right time to increase the funds in your account, but don’t ever think of it has an investment if you want to invest go look for other things to do gambling is not one of them.