The worst thing that you can possibly do is to constantly worry whether you're using enough metaphors or similies. That's a sure-fire way to make your writing stilted and clumsy. Why is it a delight to read Ozymandias [1], while the equally rhyme-peppered poetry of a young child is clumsy and jolting? It's because Shelley puts meaning first, while the student is so transfixed on their careful, perfectly rhyming coupelts that they forget what they were trying to say in the first place. The same is true of prose.
So - before you even think about if you're going to use a metaphor or some other literary device, first deeply consider the scene you're trying to paint, and the sensations that you're trying to evoke.
Take the post that you quoted as an example - I have reproduced it below for the sake of completeness. I use it not because it is necessarily a great line - or even a good one - but because I have a rough idea of what my thought process was when I typed it!
Not only that, but the typeface, layout and colours were horrendous - my eyes would lose track of sentences and slide off the page like water evaporating off a hot roof.I started out by thinking back to what the experience of trying to study from a CGP textbook was like. I think everyone is familiar with the experience of trying to read while extremely tired (if not, you will be come exam season!). That was the experience that I wanted to evoke in my writing. It's a strange feeling, and a frustrating one - rather as if your eyes are unable to stick to the page. I first considered likening it to beads of water rolling off a hydrophobic surface [2], but the majority of people would not be familiar with this image. This also doesn't quite capture the experience of one's eyes falling out of focus with page. So, the next image I considered was of water evaporating from the pavement on a hot day. I played with this image for a while in my head, first considering water from a hosepipe and then from a watering can before concluding that it's not the source of the water that's important but its behaviour.
Piecing the two pieces of imagery I'd already considered together, I arrived at the idea of water on a roof. This captures the twin experiences of ones eyes sliding away from the paper and falling out of focus at the same time, just as water falls down a roof and evaporates as it does so. In this way, I arrived at my final post.
What I want you to take away from this post is that the key to writing interesting figurative text is to take pleasure from it. You should enjoy turning images over in your head, fiddling with wordplay, and screwing about with sentence structure until your writing flows and sparkles. When you read prose or poetry, you should revel in its lyricism and its imagery. Learn from great writers, but equally, allow your own character and temperament to shine through in your work. Accept that not everything you write will be good. Writing is a skill, and as such, it must be practiced.
1: Best poem in the english language? This has got to be a contender.
https://en.wikipedia.org/wiki/Ozymandias2:
https://www.youtube.com/watch?v=4GG3j1QZFTE