Let me explain a few things first. A 24 speed is really only a 17 speed. 7 gears are redundant ones. There is a complex shifting system you could learn to avoid gear redundancy. I've developed a simpler system which is 10 easy to learn gears. It elimites gear redundancy, cross chaining and chain droop.
Long upgrades or entering uphill at a slow speed 1(1,2,3). Level ground comfort riding, rolling hills 2(3,4,5,6). Downhill, rolling hills or level ground sprinting 3(6,7,8). The only time you shift the front chain rings is when you're in 3 or 6 in the rear. Before stopping going uphill be in1(1) then use that as a starting gear. On all other stops be in 2(3) before stopping then use that as a starting gear. Shifting like this is similar to an internal hub system.
Get a bicycle computer with a cadence meter on it. Then be in a gear where you can comfortably maintain a crank rpm of 70-90. Here is a cadence meter I like using on pedal only builds or non shift kit builds.