How do you control your banks?
It's Easy, Ask yourself How big your Bankroll is? and if you Divide it by 100 then the maximum buy in is the answer, There is no use telling yourself you can deposit $100 and then start buying in for $25, because 4 games later you are back to the deposit screen giving more of your money away.
I have had days where I could not make the money no matter how hard I tried, and lost 10 straight games, but I have come back the next day and cashed in every game I played, making that money back and more besides.
But I never buy-in for more than 1% of my Bankroll, Sure it is a small investment, but Rome was not built in a day and if it's worth winning it's worth working for.
Poker is hard work, and takes a lot of patience and study. So it is with your Bankroll, Respect it, look after it, and in time it can grow, and the bigger it grows, so does your buy-ins. Don't try to Run before you can Walk, and certainly learn how to Crawl first! That's how a successful, profitable player does it.