"Bundle" service calls. If you hire an electrician to fix a dead electrical outlet one week, then bring him in again the next to finally deal with that blinking kitchen light, you're paying for two visits that could have been handled in one.
Cost: Just the extra time and parts required for the additional job.
Savings: Up to $175 for the second service call you didn't have to pay for.
Bonus: Many pros will inspect your home for free to identify any trouble spots that might be brewing.