High quality of your message
Test your links
Make it relevant original.
Make the message light, brief and direct, to the point
Offering all sorts of things in all directions might distract your prospect...
The subject must be related with your field of activity
Don’t promote holidays in the Bahamas when you want to sell the latest laptop.
Always allow people to decline receiving further messages
Update your list with the new information! The subscribing/unsubscribing option is usually at the end of the message.
Never send a message for selling something else than what you have to offer
This means don't send promotions for other products that require people to buy something. Unless you have a clear agreement with this other company.
Once a week maximum for a free casual list
Unless it is clearly specified when people sign up for it.
Don’t overload your existing clients with new promotions
This could distract them from what they are already buying from you
Have fun marketing your product
Offer the clear possibility to forward this message to friends