Use both Twitter and Facebook, and while you at it why not add a Facebook Fan page for your business and build fans to your business.
I would also recommend to make a nice Twitter background that relates to your business. You can check out my article and download a free template on how you can make a Twitter background in less than 30min, check out the how to video too.
If you don't have keynote you can use your powerpoint slides!
If you need help just contact me!