Be prepared because they can be overwhelming to your e-mail service. They are the most important so take your time when submitting and make sure your descriptions are well written.
Manual submissions take a lot of time but it can be time well spent.
When submitting to FFA sites use the multiple site submission services. These sites generate less traffic to your site because the links on ffa sites get rotated out so quickly. The key is to submit often and to lots of sites. Submit to FFA sites just before times when the internet is busiest so more people can view your ad before it is rotated out. Just remember, you will get loads of confirmation e-mails.