how to do email marketing

Write an effective subject line. First of all, we have to keep in mind the risk of being flagged as spam.
While there are plenty of ways you can ratchet up the impact of your subject lines, balance this impulse by remembering you want to maintain the long term value of your list. The maximum subject line length will be enforced by your software, but always try to keep it below 50 characters (including punctuation and spaces), because after that you are almost guaranteed to get cropped by email clients.
As a Virtual Assistant, it is a good idea to aim for much lower, a goal of 20-30 characters has worked well in my testing, and certainly those with below 30-40 characters perform much better than those above.
Ideas for subject lines are: News - Tell your recipients what’s new, something that is happening or just happened that they will want to know about,

Tips - “How to” is a great way to get your email opened, providing you connect your solution to the recipients needs, Offers.

Make a compelling offer that the recipient will want to take up and Questions,
Ask a question that the reader will answer “yes” to, or maybe put the subject in the form of a mystery or puzzle where the they will feel compelled to find out the answer.