First of all, I'd like to mention that these tips are relate to the time I'm here at Steemit (which corresponds to less than 2 weeks). but some things are very noticeable (at least in my way of seeing them) ...
#01 - Write about what you like (or find it relevant).
When you are writing about some subject that you like or are familiar with, your writing will flow more easily because the idea will pop up in your mind more naturally. Insisting on writing about what you don't like or don't know won't get you anywhere.
#02 - Organize your ideas.
It's normal to have many different ideas to write on the same subject, but the things need to be organized so that the reading makes sense (especially when the post is too long).
#03 - Write clearly and objectively.
Wanting to impress readers with difficult / fancy words won't make your post more interesting (on the contrary, it can make readers very bored). Less is more and this certainly makes the difference.
Much attention to spelling. mistakes are allowed, after all... No one is perfect (but excesses are very harmful).
#04 - Avoid using slang and bad words.
This tip seems a little bit obvious, but I've seen it happening around here. So, I think it's relevant to point that out.
#05 - Use some photo, gif or video.
Most readers are visual, so using one of these three tricks is a great way to get their attention to your posts. And remember, if the photo / gif / video are not yours, always mention the source (leaving author link, preferably).
#06 - Be creative (in relation to the text).
Writing about something that is 100% original is a virtually impossible task, so don't care if the subject has already been discussed several times because what will highlight your post is creativity as you wrote it.
Take your time.
#07 - Be creative (in relation to the title of the post).
A flashy / curious title catches the attention of many readers (remember that most of them are visual), so... Don't create a post with a very simple / not very relevant title.
#08 - Be funny and ironic.
If the subject you're writing gives you a few touches of irony and laughter, why not do it? The reading will get more fun and the text lighter (but be careful not to overdo the dose).
#09 - Excessive emoticons? It's better not.
Even though the subject you are writing offers you this freedom, the use of emoticons can make your post very childish and this will surely drive many readers who won't feel comfortable reading what you have written.
#10 - Know how to format your post.
A lazy / badly formatted text looks ugly (it may seem like a silly thing, but that counts too many points in your favor) and very uninteresting to readers. So, try to ormat your texts as best you can.
Thank you for reading and I hope the tips have been helpful (especially if you just started your career with Steemit).