Never add people to your list who have not expressly joined your list themselves. You must have their permission to send them emails.

Don't purchase lists if the list seller cannot prove the subscribers are double opt-in and willing to receive your emails.

Don't flood your subscriber's inboxes with too many messages in a short time. Be clear how many emails you'll be sending before your subscriber signs up and in your welcoming messages too if possible.

Never send more than one message per day, unless you must fix an error. People will hate you for it, you'll lose their trust and respect. You may be accused of spamming and have your entire site shut down.

Don't insult or patronize your readership. You will lose lots of subscribers in a very short time.

Never ever share, sell or rent out your list to anyone. This is a huge mistake to make and could get you banned from having a website.