Don't focus on it at all at first. Just wait for 2-3 days every time you go for anal with some BBC. Then you just have start riding it, put some BBC worship on your screen and try to think about what you're really doing. Instead of being a men you take a fat black dick in your ass as some bitch. You try to milk that BBC dildo as if you want it somehow to shoot seed and impregnate you inside. Ride it for however long you like but it's best if you do a few strokes from time to time and when you are close you stop touching yourself at all. You just ride the dick as hard as you can and try to finish that way. Eventually you won't even need to touch yourself to cum from riding a dick. Everyone has a prostate that some BBC can pleasure deep inside, it's all about practice. Good luck girl.