See above for some great suggestions. Starting small and working up is a really big help with SSTO. The most likely problem with flipping for you is that your center of thrust is not inline with your center of mass. This is very important, as the thinner the atmosphere gets, the less your control surfaces will be able to counteract any misalignment. Also be sure that your center of mass isn't changing too much throughout the flight. As it can more forward or backward of your center of lift, things can get a little chaotic. You want the center of mass to stay on or in front of your center of lift, and not deviate much from either position. Listen to RoboRay about the action groups - that is key. You should also be able to throttle down with the jets and rockets both enabled to get more use of the jets, while still getting a positive velocity change. When you drop below about 50% throttle, then shut down the jets and power up those rockets! If you need some examples of successful SSTO craft, I can post a few. Good luck.
