This is really difficult to get right unless you've done the same kind of project a few times and have code you can reuse. You also have to manage scope creep,

This is really difficult to get right unless you've done the same kind of project a few times and have code you can reuse. You also have to manage scope creep, be crystal clear on definitions and what's going to be delivered, and tactfully keep the client from trying to add big features at the margins.