Just keep doing what you're doing. It will evolve as you keep drawing and thinking. And if it doesn't, well then draw something else. As long as it's fun nothing else should really matter.
If you want, you could experiment with incorporating fancier drawings as an experiment, when it fits the situation or the joke, but you don't need to.
If you do feel insecure about your drawings, just look at early work of a lot of famous cartoonists, or just look at XKCD, which is wildly popular and by no means great art - though it does work well. Early Doonesbury and Jules Feiffer were also very rough. Everything starts somewhere. Don't worry about it.