It also helps to send an email to a scheduler for a particular project, right about this time in the month, for most companies, and say "Hey, it seems I missed out on the XYZRetail job in my town this rotation. Please keep me in mind for next month."
For new companies that you sign up with, that don't have self-assign, that you apply for a job and it's still in "Applied" status a day or so later, take initiative and shoot them an email, and say "I know I haven't done any assignments for you yet, but I have worked for # of other MSCs, and wanted to let you know I am dedicated to MSing and am committed to performing this assignment well before the due date."
It might seem like ass-kissing, but what it's really doing is letting them know that you follow up and follow through. They are more likely to take a chance on you then.
Start making a list of your companies, and their assignment release schedules. After awhile, you'll start to notice a pattern. Until then, check back often... every day, if possible, so you'll be one of the first to know when new assignments hit.
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Plan the work. Work the plan.