Tell people about it. Send emails to all of your friends, family, acquaintances, co-workers, etc. a month in advance, 2 weeks in advance, a few days in advance. You cannot remind people too much.
Mark the way to your studio clearly. If you are in a building with others, put up signs to let them know how to find you. If you are the only one in your location, make visible signs for the outside of the building.
Make postcards. Have something for people to take way when they leave your studio. It should have your name and contact info on it as well as a memorable image of your work so people can get ahold of you later. Grey Printing in Cold Spring has very reasonable rates for postcards and quick turnaround time for all the procrastinators out there
Talk to people who come in. This may fall into the "duh" category but you would not believe how many artists don't bother to say "Hi" or engage anyone in conversation. This sends people headed for the door if they don't feel welcome or comfortable.
If your goal is to sell your art, put prices on everything for sale. People are shy about asking.
Don't be offended if people walk in and walk right out again. Sometimes after seeing a lot of art in a lot of studios, burnout sets in. Its not your fault.
Bring your lunch. You might not be able to get away during the course of the day. Be prepared.
Have a guest book for people to sign. Get their emails so you can let them know about future shows.