A newsletter without subscribers isn't going to do much for you, so you do have to make an effort to build your subscriber base.

It is important to make it clear on your website that you have a newsletter and also what the subscriber can get if they sign up. For example "Sign up to our monthly newsletter and be in to win great prizes!"

To start off your subscriber list you can use email addresses you have already gathered from clients - as long as they gave you permission to use their email for sending occasional messages.  If you are not sure whether you have that permission then it is advisable to invite your clients to opt in to the newsletter list (see below for more detail on this). Your newsletter must include information about how to unsubscribe from the list - this is automatically built into the delivery mechanisms we talk about below.

The great thing about subscriber lists is that you can have more than one. You can sort your subscribers into groups (depending on how much information you collect from them) - e.g. interested website visitors, suppliers/clients, competition entrants, repeat customers, people who have birthdays in certain months and so on. Once you have grouped your lists you can target them each with more relevant information - slightly different newsletters.

Note that running competitions is a great way to boost subscriber numbers. The competition gives them a reason to sign up, and then they will stay signed up if you continue to deliver relevant content to them.