With Joist, you can request a deposit, and even allow the client to pay, right from your estimate or invoice.
Just tap Edit, scroll down to Request a Deposit and Send.
Under Edit mode you'll see this:
You can then add in the amount that you are requesting for:
Your client will see a Pay Deposit button.
If you've enabled Joist Payments they can pay the deposit right there and then -- giving you peace of mind that the project is officially underway.
For more on Joist Payments, check here for more info.