So you may have seen a video from (you-tubers name here) and thought 'Wow I wish I could do that. But you failed and thought WHY DON'T YOU WORK??? well I'm going to help you with that. Here's a few basic rules to help you: 1. It must fly like a plane and be able to turn and pitch easily. 2. The center of mass must be a TINY bit in front of the center of lift. This will help with stability in sub-orbital flight. 3. the center of Thrust must line up with the center of mass. 4. the less fuel tanks the better. when the fuel burns the CoM shifts around and will make you flip out. 5.AIR INTAKES let you run the jet higher up. also one turbo engine is easier to work with when you flame-out. 6. For first flyers Mechjeb is also very helpful because it will help you to not flame-out (engine runs out of air) 7. RCS may help to control in higher altitudes when flaps and winglets wont work as well. Engines: For your jet engines ALWAYS use the turbojet engines. They have more thrust and a better ISP where you will be needing it, in high atmosphere. For your rocket engines you can use most engines, but my favorite is the aerospike because it has good thrust and good ISP even in the low atmosphere. Using nuclear engines is not recommended because they have bad thrust and most of the time wont be able to lift you out of the atmosphere. If you want to use them make sure you have AT LEAST 1.7 km/s of speed in the atmosphere. Here is one of my creations (stock). http://kerbalspaceprogram.com/the-dragonfly/ for fuel line help: http://forum.kerbalspaceprogram.com/showthread.php/45304-Fuel-flow-from-outside-to-center-tutorial-%28COM-solution%29 good video help:http://forum.kerbalspaceprogram.com/showthread.php/39141-Tutorial-How-to-make-your-first-SSTO post more tips to improve help!