The Importance of Drilling
In class we go over techniques and then try to apply them during our fights / rolls. However, a lot of students often fall back on what they already know once the fight starts and either (a) don't feel comfortable trying to apply the new technique during a live roll or (b) simply forget how to do it when the pressure is on. This is pretty normal.
One of the best ways to understand the mechanics of a move so that you can apply it during a fight is to drill the move - A LOT. Once you understand the intricacies of the technique, then you can try to apply it during your rolls. Some aspects of the move may work while others may still fail miserably (or maybe you get lucky and hit it every time).
Don't get frustrated if a new move, or even an old one, isn't working. Keep trying it. Ask your opponent how they were able to stop it from working. Make your adjustments. Drill it more. With some patience and persistence you'll start applying the technique properly during your live rolls!
Check out the two videos below (1) of black belt, Kevin Goodwin, and brown belt, Ken Sutton, doing some of their early morning drill sequences at Team Junqueira and (2) of two of our advanced kids, Derek and Ethan drilling an entry to the triangle choke when your opponent is standing in guard.