Please note this is just my interpretation of the guidelines. Other reviewers may disagree - some of my submissions are disapproved too - so don't blame me if your posts are disapproved on my recommendations :) This is for Curie's curators.
Generally, as a curator, I look for engaging posts that I feel add value to Steem in some way. I particularly seek posts which are sure to be popular on Steem - if only they were discovered.
New and verified authors only, who have been persistent without much success. Brand new authors who have one or two posts without verification do not qualify.
Look out for authors who have made a good few posts, let's say 3 or 4. Those who have engaged with the community actively, making valuable comments on other people's posts etc. Someone new, who is into the community, but hasn't quite been discovered yet.
General guideline for "new author" would be between 27 Reputation and 52 Reputation.
Pretty obvious. Note that you can post by authors up to 52.9 Rep (which still says 52 on Steemit), but not 53.
Posts must be more than 150 minutes old, but less than 24 hours,
Also pretty obvious.
with maximum $1 pending payout.
The pending payout of the post at time of submission must be $1 or less. This is a pretty common mistake, as the submission platform doesn't enforce a hard limit.
A single author may be upvoted only once in 2 days or twice a week.
Look back through the author's profile, if they have a vote by 
Also, try to avoid authors who are writing a series or worse, trying to milk the same topic - Curie is unlikely to vote on all parts from the same series, or a repetitive topic.
Only original content.
Original content, created by the author of the post.
Articles, art, poetry, videos, recipes, etc. that appear first on Steemit.
Older reposts do not qualify. For example, an author may repost a blog from 2012, or a video from April 2017, etc. Make sure it's something new and fresh made for Steemit, within the last few days.
Please make sure sources are linked properly
Particularly for factual posts, citing sources is important.
check for plagiarism before posting here.
You can use tools like Quetext, Grammarly, Plagtracker, etc. There are plenty of options! Often, a quick Google search is enough to find a duplicate. Be wary if the English sounds funny - it might have been translated from a different language.
No Steemit-related, photography, travel, religious, introduceyourself or political posts.
Anything to do with Steemit or Steem, avoid. Religious or political posts, too. Political posts might be OK if they are historical or objective, but no political rants please.
For photography, this refers to posts which are explicitly to show off the photographs. Posts that use photographs to enhance or aid a different narrative are OK.
Same with travel, if it's the traditional travel post with pictures and sharing the author's experience, best to pass. However, it could be a travel post with a twist - maybe a video, maybe documenting an event etc. Those might be approved.
English posts only.
Some posts are bilingual. Be careful about those - they may not be approved unless the post is exceptional and the translation is original.
Finally, quality is subjective, but the curation score lists have proven time and again that this is absolutely a skill that can be learned. Pay attention to the type of posts
These are just guidelines, and exceptional posts are sometimes approved even if they don't meet the guidelines exactly. It depends on how high your CS is. If your submission limit is only 2, it's best to only submit sure-shot posts. If your submission limit is 10, I'd once again be wary. But if you have unlimited submissions, and you're doing really well for the week with 100% approval rate, it might be worth a gamble.
Hope this helps!
Some more official pointers, though this is from a long time ago.
