One of the best ideas is to pinch other people’s. Copyright law means that some work still remains to be done but in general the difficult bit is already completed. All you have to do is pick the right email to copy.
What makes a good email is all but impossible to define as there are so many variables. Good quality email marketing software will provide guidance and probably wizards to help you through the design stage but these will only be able to go so far. In any case, you do not want to be just be part of a crowd.
Subscribe to a few direct email marketing lists, preferably those in which you have some interest, and study them while trying to put yourself in the place of its target audience. Ask yourself if they fulfilled their function.
The first thing an email needs to do is to keep the recipient reading. If you became bored and disinterested then the design team failed. Do not merely reject that one as most recipients would. In order to get something from the exercise you need to work out why it did not engage you.
A tutor at my art college dissected an advertisement of mine in front of the class. He praised its overall appearance, its design and especially the graphics. The imagery was modified art deco and had taken me weeks to perfect. The tutor mentioned that the product was designed for those who would have been 20-30 in the early 50s, people to whom it would have been old fashioned.
As he pointed out, I had missed my target audience by a generation.
If the email bored you then the probable reason would have been that it was poorly targeted. A picture of a town centre busy with night life and clubbers strolling past is probably not high on the list of the picture editor for holidays for the retired.
When designing the email consider to whom you are sending it. As my tutor said, it is not the time to be self indulgent no matter how pretty the result.