Not too fast, not too slow. The optimal speed for most sedans is around 55 mph. Which means you may have to take it slower than usual on the highway, and perhaps put up with rowdy teenagers honking at you, calling you 'grandma,' and zipping off in their Roadster to go play mailbox baseball (or maybe my version of teenagers is culled strictly from the movie 'Stand by Me'). But they'll be paying at the pump, while you laugh all the way to the bank with your sweet, sweet gas savings.
Drive at a moderate speed