You need to Tweet some other interesting stuff too that preferably isn't related to IM.
If you struggle to think of things you can Tweet - here's something you can try...
Sign up for 'Google Alerts' and set your topic as 'Breaking News'. This means that Google will email you FRESH items considered newsworthy and you can pluck anything that you find interesting from it and then Tweet it.
Everybody loves a bit of gossip and your followers won't consider you a sales-maniac!
(Twitter follow me @seoknowhow)