With thinning the 2 biggest tips I can give is start early and raise your platforms. If you begin thinning while using percussion you can save yourself a lot of work when you transition to ishi and then handheld pressure flakers.
With pressure flaking, if you will setup your running platforms to look like a single beveled edge you will be able to push flakes off much easier than if the edge is in the middle.
Other than that, it's all about pressure and direction. Make sure your platforms are robust enough to take the pressure and make sure your angle will allow the flake to travel thru the stone and out without hinging.
Towers post at the top is an excellent tutorial for thinning.
Scott
