The easiest way to earn steem is by writing good, quality content. Nowadays, you can write about pretty much anything and it may become a successful post. These are some guidelines to follow if you want your post to become viral.

Take your time to write, and be original
Explore your thoughts, challenge yourself to get the best out of you, this way the reader will surely get engaged by your content and is more drawn to hit that upvote button, maybe even resteem your post. Do not copy content from somewhere else or Hive account@cheetahbot will comment on your post.
Write long, insightful posts
Try to hit at least 500 words for your post, but don't just fill it up with nonsense or else other steemians will know. Like I said, TAKE YOUR TIME and a minimum 500 words post will come easily.
Use a great thumbnail
People are drawn to posts with thumbnails, that is proven. You know when you see that post and has no picture to the left of it? Would you click on it? Probably not even though it may have great content inside. Best way is to make a thumbnail yourself, learn to use GIMP and create a killer thumbnail yourself. If you're not that good with a graphic design software, find a thumbnail on the internet that is related to your content and that will get peoples eyes so they will click on your post.
Use lots of images in your post
A wall of text isn't fun for anyone. Do you think Hive account@sweetsssj made it big by creating posts about traveling and culture without using images/photos? Not really. Use them between paragraphs, use them in the beggining or at the end of the post, images will enhance the overall quality of your post by a lot.
Best image hosting sites that I personally use are Postimage and Imgur. With these 2 websites, your images will never expire.
Format your post
A post can have 10000 words and be of the utmost quality, people will not read it if it's poorly formatted. Take your time to structure your text and images, people appreciate it and increases the chances they will fully read it. Use Mastering markdown or this post by Hive account@thecryptofiend to learn how to make lists, tables, bold or italic text and much more.
TAG smarter
Tags are extremely important for a post; without them, your content has no chance to be found after the first few seconds it is shown in the New tab. You can use up to 5 tags, the first one being your main category and the most important tag.Try to use your tags responsibly and relevant to your content.

You can also check the trending tags HERE to see which tags have the best payouts and which tags have the most posts or comments.
Currently, the trending tags are:
Trending tags for the highest payouts

Trending tags for the highest number of posts

Trending tags for the highest number of comments
Catchy title
Write a title that isn't too long or too short that is relevant and that will catch the eye of steemians so they click your post.
Create a series of posts relevant one to each other
For example, if you post recipes, you can add #1 at the end of the post's name and in your next recipe post, put #2 and so on. You get the idea. It makes it easier for people to follow your posts and it also converts some of those readers to follow you if they are interested in that subject. Check Hive account@sweetsssj for a perfect example of a post series.
Post introduction
Always try to write a small introduction at the beggining of your post. Don't just summarize your entire post, but do it just enough to make the readers want to keep reading. Try to do it in 1-3 sentences.
Call to actions
People click your post, read it and move on, that's the most often case. You can use call to actions by adding an image, gif or even text at the end of your post reminding people to upvote, comment, follow or resteem your post. People just forget to do these things, not that they don't want to. You can even add some links to some of your other posts and if they click it and like that content, you can easily gain another. Another easy call to action is to ask your readers a question at the end of your post, for example: What do you thing about X?. This way, they will be more drawn towards commenting on your post.
Try to reply back
This one's easy. If someone commented on your post and that comment is extremely relevant to your content, they actually took the time to read your post. Try to reply back to them, at least with a Thank you comment. Engaging this way will help build your following.