Fill out your FAFSA. This takes about an hour, and is necessary to get any form of financial aid or Federal student loans. You'll need your 2007 1040 (and your parents, if you're a dependent) and your FAFSA pin. Once your FAFSA is completed and accepted, it takes 3 days to 4 weeks for the government to process it and send the results to the school(s) of your choice.
Double (and triple) check your schedule. Ensure that you don't have any conflicts, and that it will really only take you 10 minutes to get from that one class to the next.
If you're employed, take the schedule from above, adding travel times to either end, and give that to your employer to alter your availability. If you get your new hours in ASAP, they won't have any reason to call foul when you can't work a noon to five shift.
Contact your professors. Ask them about specific materials, especially books (note their ISBNs). Keep a well organized list of everything you'll need to buy.
Check the prices on your books. Look at websites such as AddAll.com which will give you a comprehensive list of which other sites currently stock the book (and for how much).
Secure your financing. If you need private student loans, get the paper work going about 4-6 weeks before classes begin, to ensure you have the funds on time.
Buy your stuff. Once you have the cash, work down your list of materials and books. Put everything in a designated area to prevent mix up/losses.