How can home service businesses improve profit margins without raising prices?

If you aren't raising prices, you can only cut things. Take a hard look at your expenses and see if there are things you aren't using. You might be over paying your people. Maybe you can make a performance pay system and reduce their base, but make the potential to be higher. Bottom line is if you aren't making money you need to change stuff. If you're not willing to raise your prices then that's going to be the thing you cut.