Every job you do promotes you. When you do good work, people talk about it. Amazingly, there are a lot of people, and companies, who "flake out" professionally. That, unfortunately, is common. But you can compete successfully against them simply by promising a lot, and delivering even more! And that means everything relating to the job - every detail - returning phone calls, emails, and just plain seeing the job through. And since there are only so many hours in the day, those hours that you do have need to be devoted to doing a good job.
And if your time-and-money budget is tight, then give your clients everything. In return, they will give you the best advertising there is - word-of-mouth.