You are ready to launch your heavy 3-stage rocket to send multiple payloads to Lunar orbit and beyond when you realize you are about 5% short to orbit. How do you get that 5%?
The best idea is to add stages, or get more powerful ones through completing missions. However, the stages have finite power and at some point the rocket is so top heavy that an extra stage will knock off the -et and make your ship a rock. Or maybe you just want to have extra fuel in your tank for that final docking stage. Then you need to up efficiency. This is basically just making as much of the fuel into energy as possible, and as much energy into altitude as possible.
Due to the fact that the first stages in Space Agency are required to be lit while the sparkers are firing, it is a good idea to start the engines at around -0:05 .
If you are burning the engines when the rocket is at maximum speed, the extra thrust goes to waste. So, if you are burning a stage that has engine restart, cut engines when at the top of the velocity gauge and restart when the velocity falls to green. Also, prepare to glide at engine cutoffs. Before gliding, tilt the pitch up.