A good lawyer will make it a point to send out confirmation e-mails or call clients ahead of a scheduled meeting. Doing so will deter the client from cancelling last minute, and will show how truly invested you are in the case.
Let the client know that yours and their time is very important, and a speedy case is beneficial to both parties. If they are serious about their legal matter, they need to respond to the confirmation e-mail within 48 hours of the appointment. If they do not, you should fill the slot with another appointment with a committed client.
In doing these steps, you eliminate time wasted on flakey clients, and make space for clients who really do need your legal expertise. In a worst-case scenario, you’ll have a client who has forgotten to confirm come in anyway. It is important to still act professional in these cases, and politely let the client know they need to confirm in the future.