Here are some common mistakes that others make:
1) Uncooperative website.
You are fixated on your open rates and miscellaneous metrics, and forget to make sure your sign up "call to action" is visible on your website. Or your web developer is not your friend.
2) No promises.
You ask people to blindly opt-in without providing compelling reasons for them to do so.
3) Overly nosy
You ask way too many questions on your opt-in forms.
4) Being shady
You don't provide a privacy policy and/or don't detail what you will and won't do with your subscribers information.
5) Not seeing other opt-in opportunities.
You did not include everyone in your organization on your opt-in strategies. Front desk, support desk, accounts and admin, networkers, telemarketers....the list goes on.
6) Badly designed offline opt-in forms
You provide little scrappy forms at your front desk that do not provide enough space for email addresses.
7) Unfinished business
You don't add opt-in's collected from your offline forms because they are a pain to decipher. You may find that they have piled up so much that it may be 3 months later that subscribers are finally included.
8) Crappy content
You provide such crappy content that no one wants to forward your emails to their friends.
9) Really crappy content
You provide such crappy content that people unsubscribe in droves.
10) Simply hostile
You go with one click unsubscribe, and have no strategy to persuade anyone to stay a bit longer.
"Here's another e-zine you might find more relevant"
Well done! You've just done yourself out of a job.
-- What else are you doing wrong? Let's make this list grow to 20 points.