1. Post what would be of interest to you if you were a customer or business partner.
2. Be spontaneous - tweet about things that are happening right now.
3. Add a photo - we are all quite nosey, so most clients will click to see a good picture of an event, PR shoot, an award you've won etc.
4. Keep it short - you needn't always use the 140 characters - brevity is good policy.
5. Research hashtags relevant to your business sector and include them regularly as they will help you get noticed by potential customers/clients.