The filtering effect is the benefit people underestimate. A prospect who agrees enthusiastically and then hesitates at a deposit was frequently not going to proceed, and finding that out before you schedule the work is worth considerably more than the money. Deposits convert uncertain interest into a decision.
Frame it as process rather than as a condition. A sentence in your proposal saying work begins on receipt of the deposit, followed by the schedule, reads as how things are done. The same request raised separately after somebody has agreed reads as a concern about them specifically, and produces a different conversation.
Size it against what you would lose if the project stopped after the first phase, rather than against a conventional percentage. For most service work that lands somewhere between a quarter and a half depending on how front loaded the effort is. A figure tied to a reason is easier to accept than one that appears arbitrary.
Stage the remainder against milestones rather than dates for anything longer, since money moving when work completes protects both parties. You are not funding months of effort, and the client is not paying for progress that has not happened. It also surfaces scope disagreements while they are small.
Treat the deposit as unearned until the work is done, which is the discipline that prevents a cash flow problem. It is money against an obligation you have not yet met, and a strong month that was actually prepayment leaves you delivering work with the money already spent. Knowing how much of your balance is unearned matters.
Make paying it trivially easy, with a link and a clear amount rather than bank details. A deposit requiring somebody to arrange a transfer at the moment they decided to proceed introduces friction at exactly the wrong point, and the delay is frequently where enthusiasm cools.
Handle an objection as information rather than as an obstacle. Sometimes cash is tight and a smaller first stage resolves it. Sometimes they have been let down before and want to see something first. And occasionally it means they cannot commit at all, which is considerably better to establish before the work than after.
Then be consistent, because inconsistency is what creates the awkwardness. A business that takes deposits from everybody has a policy. One deciding case by case is making a judgement about each client, and clients talk to each other.
Confirm receipt in writing along with the start date, since the transition from agreement to work beginning is where clients most often feel uncertain. A short message acknowledging the payment converts a transfer into a commencement.
Decide what happens if a project is cancelled after the deposit, and state it, since that is the clause everybody avoids and the one that produces the awkward conversation. A stated position, whether retained or partially returned, is better than improvising.
Invoice the deposit properly rather than requesting a transfer informally, since that produces the record both parties need and it makes the accounting straightforward when the balance falls due.
Keep the amount proportionate to the work rather than to your cash needs, since a deposit that covers most of a project transfers the risk entirely to the client and reads accordingly.
Ask for it at the point of agreement rather than later, since the willingness to pay is highest at the moment somebody decides and it declines with every day that passes.