Enlist the help of some eager volunteers, who can donate treats and also help with the sale.
Assign each volunteer to a special task: handling publicity, organizing donations, setting up the sale, selling goods, collecting money, and cleaning up.
Create a participant/donation signup sheet (make sure there's a place for contact information) - this will help keep track of what people will be bringing and prevent duplicate items.
Be clear with volunteers about how to package their baked goods. Use disposable baking tins and ask them to fill out a bake sale tag - list the recipe name on the front and the ingredients on the back.
Determine a time and location for your sale. To guarantee that lots of people will attend, try to plan the sale around another local event: garage sale, school play, sporting event or even a craft show - of course, you'll want to get permission from the other venue ahead of time.
Get the word out! Create signs and fliers with all the pertinent information and post them where people will see them: supermarkets, the local library, the office, the gym, and around your neighbourhood - make sure you have permission before posting anything.

Have a jar or a box ready to collect the money. Don't forget to have some change available. Keep track of how much change was originally in the box, so that it's not accidentally added to the profit.
Create signs to display at your sale, include: the name of the sale, item categories and prices.
On the day of the sale, set up your table and chairs. Spread out a table cloth and place your baked goods into categories or serving sizes. Individually-wrapped items (cookies, brownies) are usually placed in the front and larger items or items that have to be sliced (cakes, pies) are easier to handle in the back. Also consider using boxes or tiers to create a nice presentation.
Don't forget to also bring: knives for slicing, spatulas for serving, paper plates, plastic forks, extra plastic bags, for those who wish to take their goodies home, and miscellaneous items: cooler for any perishable items, trash bags, paper towels, moist towelettes or wipes, napkins, tape, scissors, paper, and pens.