Good suggestions from rogierb, but by wasting their time on Facebook, are you meaning you just dont want your employees screwin around and not working all day? Set up a proxy or some sort of web filter. They will hate you for it though 😊 Same as I hate the place I work for blocking half the damn internet. Something like Websense (what we have here) will allow you to set up quota time for things. for instance, you can set that they have 2 hours per day of time to visit sites like Facebook or something like that. Once that time is up, its blocked until the next day.
Adding to rogierb.. keep up with a good schedule. Use, god I hate to say these words, Microsoft Project, or something similar to break every piece of the project into tasks. Assigns roles/tasks/responsibilities to resources (employees). Set everything to a timeline and make sure they are staying on track. As mentioned, provide incentives for getting stuff done ahead of schedule.