Present yourself like you know what you're doing. Let people know that you've got your business game together and that you're not messing around. Present a consistent image across all your media and people will know you mean business.

Letterhead, envelopes, presentation materials...

These may be little things but it's the little things and the details that set you apart from your competitors. Let customers know that you sweat the small stuff and you're all in when it comes to your business.