A welcome with a practical purpose
Read the first message a client receives after accepting your service. It may be warm and well written while still leaving the next step unclear. Look for the action the client is expected to take and give that action a clear place in the message.
Start by confirming what has been agreed, using the actual service name and scope. Then explain the immediate next step. A new client should not have to reconstruct the process from a proposal, an earlier email and an attachment before they can begin.
Ask for what you need now
A long request for information can be difficult to complete when the client does not know why each item matters. Group the requests by purpose and explain how they relate to the start of the work. Separate information needed now from material that can follow later.
If an attachment or form is part of the process, make its role clear. Tell the client where to send a question and who will respond. Confirm any stated timing with the people who will actually do the work before the message goes into use.
Read the handoff from both sides
The client needs a manageable next step. The service team needs the right information in a place they can use. Review the message with both needs in mind, including what happens when the client sends only part of the requested material.
A useful welcome can remain brief. Its job is to connect an agreement with the first piece of work. Once that connection is clear, the tone can feel like the business: calm, friendly or formal, depending on the service and the relationship.