I think a good next step would be Expert Card Technique (again by Hugard & Braue). If you've got a bit more to spend then go for the Card College series. You'll already be familiar with the material in some of the early chapters so you'll be able to get through them quite quickly, but I reckon it's always useful to properly instil the fundamentals into yourself, look at them from various angles, work out for yourself why you do certain basic things (like, why use mechanics grip rather than have all four fingers on the side of the deck?). This really gives a good grounding and helps you learn more complex things quicker.