Is it alright to post first and tag later?
Or is it better to apply all the tags, then post?
I've seen contributors do both, and don't know which is more efficient.
Posted under General
The official stance is that as long as your posts are fully tagged within a reasonable timeframe (no longer than an hour), you're not breaking any rules.
My opinion, however, is that it's better to fully tag your uploads before you press the Upload button. This makes it easier for other users to contribute their own tags based on what is missing.
One reason an uploader might tag after uploading is to prevent upload sniping. The image is first stored as a media asset, which could be viewed by others if they know how. There are records of at least one user viewing other's media assets, then uploading a superior version of the post. This may reduce the chance of the first user's upload of being approved. This can also happen if two users coincidentally upload at around the same time. You can see cases of one-upping discussed in the Upload Feedback Thread (topic #7934).
Most of the untagged recent uploads I've seen have been fully tagged within a minute, so it shouldn't cause problems in most cases. However, you should always add at least the sexual and censored tags so they can be filtered out by users' blacklists.