1. Ads on the site
2. Site’s design
3. Site’s PR (unfortunately)
4. Site’s niche (weight loss, loans, insurance site get least approval – 10-20%)
5. Affiliate links – amazon / ebay affiliates are not liked.
6. Top level domain or subdomain
7. Keywords in title (any repetition, too many words etc. might get less approval rate).
8. Description – short descriptions get less approval rate, descriptions with phone numbers, URL inside descriptions are also not liked by many.
9. PR of the directory (higher PR directories have lots of submissions everyday and can take many months to approve, they tend to have higher rejection rates), newer directories approve faster.

10. Category of the site. Some sites have a ‘clear cut’ category and there is no confusion. Shopping -> Clothing type of categories are probably the easiest, others are quite ‘vague’. Locksmiths, janitors etc. can go in shopping -> home & garden -> trade services or business -> services the directory editors might disagree with submitter’s choice.

11. Directory List – if a directory list doesn’t remove directories that are ‘obviously not approving links’, the approval rate can go down.

Approval depends on a lot of factors, some of them are below:
– Selection of title (are you using too many commas in title? Are you using repeated keywords?)
– Description (is it a description written in third person narrative or it’s a string of keywords or it’s a sales pitch)
– Category (typically loans / insurance categories see a lower level of approvals)
– Email used (if you use gmail or yahoo accounts for submission you can expect slightly lower approval rates)
– Adsense / affiliate links on site (if you have a lot of pop up ads or adsense units, quality directories won’t accept your submission)
– Your website’s PR (unfortunately some directory owners think PR2+ websites are quality websites and they only approve those)

Hopefully if you keep the above mentioned factors in mind, your approval rate can increase.