You can maintain playing very well without having 200+ apm. Generally if you watch replays and see people at 250+, they've just hot-keyed 2 things and are rapidly going back and forth between them, generating ridiculous APM. APM only comes into play at very high levels of skill where macro and mechanics are equally solid from both players. But, if you really do want to get it up higher, practice your mechanics in a game against nobody. Get a small group of units together and practice moving them around the map while still producing and making workers. After you're comfortable with that, experiment with adding in buildings aswell. The best advice i can give though is to not look at apm as any gauge of skill whatsoever. Practice fundamentals and higher apm will come naturally.