Always put your contact details in a logical location, in bold type that is easy to read and easy to understand. It can be very frustrating when you are reading a brochure and it's nearly impossible to find the contact details for the company that produced it. Surely, getting a customer to call is the entire reason for producing the promotional material in the first place.
I have an older friend whose eyesight is starting to fade. He constantly complains that he can't read the text in a lot of brochures and advertisements. If you are targeting an older clientele, remember this point and make the text easy to read.
Nowadays there are many ways to contact a person: faxes, telephones, mobile phones, letters, e-mails and probably a few more, such as the carrier pigeon that may make a strong recovery one day. If you have access to all of these gizmos, make sure that your customers know about them and which one is the best for them to use to contact you.
Another important item to include in your promotional material, especially if your customers will visit your place of work, is what hours your business is open. For the sake of good customer service, the easier you make it for your customers to contact or visit your business, the more satisfied they will be with the over-all experience.