I found it was easier for me to roll foward standing than sitting. I was taught to stand with my Left foot out, toes pointed to where I want to roll. Your right foot should be behind you.
Next bend over "not kneeling" and place your left hand on the mat on it's side. Your fingers should be pointing back twords you. It looks like a karate chop " but pointed at you"
Then start leaning foward until you feel your balance start to go. Tuck your head and enjoy the roll. Just let your weight bring you over.
I used to be the slowest one when doing rolls. I would be holding everyone up while they waited for me to roll out of the way. now I'm a rolling machine! heh just stay patient and let your body remeber how to roll, we all did it when we were kids, I think we tend to think to much about it.