There are a bunch of great videos on youtube that will help. Losing width while thinning is inevitible, a palm-sized spall will often yield a fairly small point if it's got some thickness to remove (most do). You have to have the right platform angles and strike at the correct angle to take good thinning flakes without losing a lot of size. If your flakes aren't going past the center of the point, you're losing width faster than you're losing thickness. Practice, practice, practice. Watch the youtube videos. Destroy a few tons of rock and it will start falling into place. If you can make it to a knap-in and watch people knapping in person, it will help a lot, too.