Here are some ways to encourage activity on your Twitter business page:
Try to post questions that your followers may reply to. “What is your favourite colour?” might be a simple enough question and is something your bored followers may happily respond to.
You might find that a large percentage of your followers really like green, but your latest product is only available in red and blue. Is this information useful to you? Do you think selling a green product might be more popular?
You can also ask questions directly about your products. What do you think of our latest design? Is anyone pre-ordering our latest game? which model of our products do you own? etc.
Many companies run contests for their Twitter pages, often involving retweeting about the contest. If you happen to be running a contest that involves retweeting, make sure that you have enough space in your 140 character message that will allow RT@Username to fit into the message.
When holding a contest, try and make the contest one that will encourage people to follow you. there is no point in having a contest and giving away money or products if you are not somehow expanding your brand out towards new followers/customers.
The guidelines for contests on Twitter are an essential read, giving suggestions on what to do and what not to do.