I know Safelist are far, far, far, more productive than the traffic exchanges for me I do still keep a few sites going in the TE’s but most of my time is with the list builders!!
I guess for my Top Don'ts are:

People not putting their name in the email ad they send..

Their email being more than 3 short paragraphs>>>>

Things I do for better performing ads ..

I hear some say that content or subject doesn't make a difference not true at all.

Use a tracking system to see what is happening with your email and sign ups. I do I have found that with a good email ad I will get 50% of my sign ups from the body of the email and by changing the subject line I can increase the number of people opening my emails even in credit based mailers. I'm a member of a lot of Safelist so I get a lot of email no way I can read all of them and a lot I will just click the link for credit but if the subject line is good I will read the email as long as it is not a book.

Anyway just a little on my thought on Safelist / List Builder Marketing.

Here's My top performing safelist:

The Lead Magnet

List Surfing

List Adventure

Adchiever

Viral Mail Profits

I picked these based on the Sign ups and the profit I make from the sites.