One of the best bits of advice I've received from several fellow business owners including Jonathon Hinshaw of Ebway Creative is to 'Get Out There'. This means getting out of your office and going to meet people whether they are potential customers or just other business owners. You probably know the benefit you get from talking to your clients, benefits that go both ways so why not utilise this as part of your promotion.
Last time we looked at email frequency and identified that the frequency of sending newsletters is dependent upon your business AND your customers. This is why we spend time with our clients to determine who their customers are and then identifying what their needs are. If we recognise our customer's different needs then we need to take this into account when determining our newsletter lists.