A no-show doesn't just cost you one session. It's a slot you could have given to someone else, a member of staff standing around, and a client who's out of the habit of coming in. The good news is that a few simple habits make a real difference.
1. Let clients book when it suits them
Plenty of people decide to book a session late at night or on their lunch break, when your phone isn't being answered. If the only way to book is to ring, some of them simply won't. Online booking catches those people, and it takes pressure off the front desk too.
2. Remind them before they're due
Most no-shows aren't rude, they're forgetful. A short text or email before the appointment gives people the nudge they need, and makes it easy to rearrange rather than just not turn up. That way you get the slot back in time to fill it.
3. Ask for payment up front when it makes sense
You don't need to take payment for every booking, but for some it's worth it: new clients, long slots, or anything booked well in advance. A client who's already paid is far more likely to turn up. The key is being able to set that rule once, rather than deciding at the desk every time.
Small changes, full diary
None of this is complicated, and you don't have to do it all at once. Start with reminders, as they're usually the quickest win, and build from there.