For a successful open house here are some helpful tips:
Pick a theme - Pick a theme that is popular at the time and tie slogans, decorations, etc. to the theme.
Be Creative - Do something you would not normally see or do at your type of store.
Have refreshments - drinks (alcoholic or non-alcoholic) and light fare often bring people in and often does not have to be that expensive or elaborate.
Decorations - Decorate in a theme and change from what you typically have. Bright, loud or contrasting often draws attention.
Use your customer list and mail, email, or facebook them to inform them of the event. Make sure you tell them to invite or tell their friends.
Do demonstrations or provide informational tips at various times.
Bring in a celebrity to meet, sign autographs or do demonstrations.
Have special discounts or reduced pricing.
Give some small gift or have a raffle.
Provide a fun atmosphere with music - live or recorded - to make people feel festive.
Promote, promote, promote - Make sure from the outside of the building people know something is going on inside: newspapers, websites, Facebook, Twitter, radio, TV, other businesses, etc. are all ways to make people outside know you are doing something in your business.