What would be the best way to get into shape to do BJJ?

I live in Texas and my friends cousin does Gracie Barra BJJ, and it looks cool and stuff and I wanna do it. But I weigh 165 and im chubby but kinda in shape and aggressive because I play football but I kinda wanna do mma and stuff but I need to get in the best shape for it. So I need the best way to get in shape for it. At the school there is a Track and weight room. Im putting up about 145 on bench and my squat is 150 but i have ashtreschloters diesease in my knees so i dont care for that.