When asking for a deposit professionally, it's important to communicate clearly and transparently with your client or customer. Start by discussing the details of the project, including estimated costs and timeline. Once both parties have agreed on these aspects, you can then explain the need for a deposit to secure your services and cover initial expenses. Be sure to articulate the deposit amount as a percentage or fixed sum, without being excessively demanding or pushy. Emphasize that this is a standard industry practice and assure them that their investment is protected.