Simple. Never repeat your mistakes. If it is still difficult, never stop whatever you have changed in your life. For example, you don't go out with other gender alone, then never do it again. Never. Never repeat your mistakes, what's more when it is related with Allah's law. I'm not that good either, I'm terrible, that's why it is very hard for me to memorize, but at least I have that ego as a barrier to me from repeating any of my HUGE mistakes that I have stopped doing. Good luck. ;)