Do you mean the process itself?
ie setting up a Newsletter on your site that will email your database list of clients?
How do you get your emails to work for you as a business, to be successful?
There are many solutions from paid 'auto responder' services like aWeber and Mailchimp, as well as plugins for Wordpress sites in particular.
I prefer to give my clients control over the Newsletter from the site itself.
The key is to have a consistent mail out.
So many people start with a bang, emailing their subscribers frequently to start with and then drop off.This is not good.
In my opinion, you are better to commit to once a month and follow through.
Also, these days, you must be sending them real information that they find valuable- BEFORE you start asking for the sale.
Tip: Best to also minimise colours and images in your emails, as a lot of SPAM filters are triggered by those and the system admin.
Hope this helps.
feel free to contact me for assistance.