I am currently talking to a few potential clients about taking on near work in the near future, once I finish I current project, which has roughly four weeks of work left. The issue is that I only have the availability to take on one of the projects, but I am not sure how to proceed with these clients. I don't want to brush one off in case one prospect does not come through, but on the other side I don't want to end up over promising my availability and end up overbooked. How should I proceed with these sales?
Before a project is approved, you can talk about how long the project will take to complete. You can also say: if you sign off on the project today, I can start the project on X date. Please understand that I have other projects pending approval, and if I receive approval for one of those projects first, your project start may be delayed. This usually also encourages someone to get approval done.
Once that first project is approved, I always let other customers know when discussing their projects that I cannot start them right away. I usually say something like "I am currently scheduling new work to start in X month, as I am fully booked until then."
While it is possible they will take their work to someone else, this hasn't been my experience. My customers will almost always wait for me. But I have built up a lot of rapport with my clients, and finding another developer who is experienced and trustworthy isn't a simple thing for them.
You can either do what Avonelle suggested, or simply pick the most interesting/profitable one. Then try to postpone others to after than one. you may lose all of remaining but you may also preserve one.
Or you can do what I do: have a good freelancer at your disposal (from the same field) and give him the job and you take a certain percentage for being the middle-man.
You may also try, what I never did, to tell them that there are 4 projects in the queue and see which client is willing to give you a hire rate (since it's obvious you're good when 4 clients are fighting over you).
Agree with Avonelle. Freelancing is pretty much a first-come, first-served business. There will be times when this burns you—you take on a bad job that precludes you from taking on a good job offered the next day. Conversely, you may find yourself blocking out time for a promised job that never arrives—I don't do that anymore.
The only alternative is to sleep less and cram everything in, although the quality of work usually suffers when you do that, and in the long run, it doesn't pay.