Hi,
I have to say that with all the best teaching in the world, the classic' is one of those moves that reqires the performer to be a relaxed and for want of a beter word 'sorted' individual.
Knowing what to do will not help if you haven't got that quality of relaxed confidence.
The best classic force I ever saw was by my Father, he wasn't a magician, he liked magic (grew up at the time of St georges Hall etc) and knew a few 'magic uncle' type tricks. He REPEATEDLY forced cards on me as a child, then explained as best he could how it worked, basicly just give them the one you want!!! Then proceded to succesfully force cards on me again! I just have not seen anything like it since, and no I'm not able to emulate him.
I think the best magician classic forcing I have seen (haven't seen everybody of course!) is Paul Daniels, who is so comfortable with the move he has used it on live TV, again a relaxed and confident individual.
I can classic' but nothing like the level of surity and confidence of these guys.
Just keep practicing, remind me to mention dads 'fingertip coin vanish' sometime as well
Cheers
John