Unlike most other advanced techniques, you don't have to be athletic or play at a high level to develop great serves. Anybody - yes, that means you - can develop great, even world-class serves. They just need a little TNT - Technique, Necessity, and Time.
You have to have proper serving Technique. This means working with a coach or top player. Unlike most other techniques, serving is subtle and is tricky to learn by just watching. Half the point of serving is making it look like one thing while doing another, so unless you are an expert, you might not realize what's really happening. Here's my article Ten Steps to a Great Serving Game.
You have to decide it's Necessary. Top players often develop top serves out of sheer necessity - if they don't, they won't become top players. So you have to ask yourself - how necessary is it for you to dominate against your peers by developing great serves? Better serves also means you play at a higher level, and so play higher-level competition, which pushes you to an even higher level. They also lead to lots of balls to attack, which develops your attacking game, which improves your level even more. So . . . is developing great serves necessary? Remember - Anyone Can Be Very Good At Something - and (to reiterate the above), "If you develop one aspect of your game, other parts will follow. If you develop a very good serve, then you get lots of follow-up shots, and so you develop a very good attack."
You have to put in the Time. That means practice, practice, and more practice. But it has to be meaningful practice - if you just practice low-level serves, you'll end up with very polished low-level serves. Here's my article Practicing Serves the Productive Way.