These are the submission guidelines as of 05/16/2011, and are subject to change. 1000notes.com currently has several thousand submissions which have not even been reviewed, so if your post doesn’t show up it’s more then likely because it hasn’t been seen.
Guidelines for Submissions:
1). Must have 1,000 notes or more. (10,000 notes or more for the 10Knotes blog
2). Must be a follower to submit.
3). Must be safe for work. Nudity will never be posted.
4). Must not be inflammatory in either a political or religious sense.
5). Must have redeeming value which justifies it’s being featured as the ‘Best of Tumblr’. Examples of posts which often obtain 1,000 notes but are largely without substance are posts that begin, “Reblog if…”, and posts regarding the amount of ask messages one has. If there is an element of humor or creativity in this type of post this rule will likely be waived.
6). You may submit a post link to both the 1000notes blog and the 10knotes blog, however I will not post the link on the 10knotes blog if it was featured first on the 1000notes blog; the link must have been reblogged to the 10knotes blog first, in order to be approved for posting to both blogs. The reason for this is because the 10knotes blog isn’t as popular, so there will be a large number of people who haven’t seen it if it is subsequently reblogged to the 1000notes blog. However, if it’s first posted to the 1000notes blog, most of the followers of the 10knotes blog will have already seen it.
Following these guidelines will give you the best chance of being approved.