Get your location, set the date and time
Ask your best friend if she'll stand up with you...the groom is on his own! Skipping the Bridesmaid Chorus line simplifies planning since you only have to shop for dress/shoes/hairstylist for yourself and one other girl. Find a photographer (try the local college...a senior photography student may be available on much shorter notice and will be thrilled at the opportunity)buy a bunch of one use cameras to let guests take pics, too.
(If you have the wedding around 1 0r 2 in the afternoon, you can have just champagne for the toast then cake, punch and finger foods without looking cheap at the reception, much easier than dealing with finding a caterer on such short notice)
The dresses should be chosen and ordered as soon as possible, to allow for any needed alterations.
Do your invitations (Craft stores and office stores have some beautiful "do it yourself" invitation kits...get one more package than you think you'll need to allow for a couple getting messed up. Mail them 4 to 6 weeks before the wedding.
Visit bakeries and grocery stores to choose and order your cake (many grocers can make a cake just as beautiful as the fanciest bakery for a fraction of the cost and in far less time)
Also at the craft store, they'll have pretty little favors and lots of different ways to decorate or package them. Consider the possibility of using silk flowers for decorations, then you'll only need a florist for the Bridal bouquet and groom's boutenierre (I'm sure that's spelled wrong.
All that should keep you busy until a month before the wedding... Get the rings and the license.Send the groom and his best man to get measured for their suits and to reserve the ones they choose (If you can't trust him to dress himself....?)Reserve a big punch bowl and glasses at a party rental place.
Get the dresses so you can try on the shoes underthings with the dresses (you don't have time for mistakes or changing your mind!) make any needed appointment for hair and nails.
By now you should have some idea of your head count... buy the ingredients for punch, figure on a quart per person, plus a gallon to be safe. For the champagne one bottle per four guests should allow for two glasses of bubbly per person, plenty for the toast...you don't want folks tipsy in the middle of the day any way.
Hit a deli to order cold platters, they can advise better than I can what quantities you'll need....buy the pretty paper plates and napkins.
One week before the wedding, the bridal couple should go out and do something that has nothing at all to do with the wedding.
BREATHE!
All my best wishes for a lovely day and a long and happy marriage.