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There is some info on that in the FAQ. Technically there are no restrictions, but Steemit may take down anything illegal from being displayed on the website. (Technically it is still stored in the blockchain though.) If you post anything 'not safe for work' you should use the "nsfw" tag as one of your tags. Plagerism is also frowned upon, and will likely get you downvoted.

Hope that helps :)

I have one further question.
Say, in my early days on steemit, I made a post with 2-3 tags. It came with not much success.... very few votes/comments, mainly because as a newbie I had very few followers.

Later, once I learned more, got more followers, and even figured out a few other, possibly better categories/tags - I have intention now to put the same post published once again.
With little or non additions.
Will this be considered a bad etiquette? Shall I avoid doing this?

https://steemitimages.com/0x0/https://ipfs.pics/ipfs/Qmav1AHfmMgannHxKEnErU3UwfZiSbYUgCi9N8gWWkyJtd

It is considered bad etiquette, but if you do it once and a while with your very best work, and mention that you are doing it and why you think it is worth reposting - I don't think it is horrible. The main thing is we don't want the website spammed with the same articles over and over again.

OK, thanks