Booking shoots is super easy! You can speak to people about a potential shoot and get them penciled in the diary. Booking shoots is the easy part. Getting people to pay for them is a little trickier.
There's a huge temptation to let people off from paying a deposit. This is especially true with friends. You'll be able to book more shoots for sure, but no deposit essentially means no commitment. If a client cancels, not only will you be out of pocket, you'll have wasted time. Time that could have been used elsewhere.
I have personally done this a couple of times, and I've learned my lesson. One being a wedding. I booked the couple in with no deposit, refused another (and more expensive wedding for the same date), only for the first couple to cancel two weeks beforehand. I was pretty annoyed, but it was a good learning experience.
A deposit also gives you confirmation of the date being booked. With multiple clients asking for the same day, it's good practice to inform potential clients that the first to pay the deposit secures the date. It sounds a little brutal, but business is business.
For weddings, I used to ask for a non-refundable 10% deposit upfront, with the remaining balance to be paid two weeks before the date.