Come up with a killer subject line. This is your one change to have your customer open your email and explore further. If you don't nail this step then you have lost them and the email was not successful.
Most of your customers will be busy people, not many of them will take the time to ready your email word for word. You need to set up and design you email so that key information is noticed and ready as your customer scans the screen. They need to read your message in as few words as possible and know what is required of them.
If you don't know then you can have a pretty good guess at how many emails a customer must receive through their inbox each week. You are in direct competition with every other business that has decided to automate their email marketing. You need to stand out...your content must be compelling and exciting and it must appeal to the customers you are targeting with your email campaign.
If you don't tell your customers what they need to do...they will do nothing. You must include a CLEAR call-to-action in your email. Tell your customers what they need to do, by when, to achieve x and save y. This will turn leads into sales and help improve your sales figures.
You need to know if you are hitting the mark. Measure the results of your automated email marketing. If something needs tweaking, make the change immediately and improve for next time. Ask your customers for feedback, after-all they are the ones you are targeting.