The Oberth effect is interesting. You want to get as low/fast as possible (converting your fuel's gravitational potential energy into kinetic energy), and then

The Oberth effect is interesting. You want to get as low/fast as possible (converting your fuel's gravitational potential energy into kinetic energy), and then do a burn to harvest that energy, dropping the exhaust into the sun while the spacecraft zips away at high speed. It's basically the "tennis ball on a basketball" trick, with rockets.