That is: Describe a scene with a suitable atmosphere, include various descriptions of plot objects and misc objects. Include visual (smoky room etc.), audio (conversation, clink of coin/mugs), olfactory (the smell of smoke/tobacco/unwashed bodies) and tactile (the sticky floor from beer spills) senses. It ought to include obvious things (people, potential dangers, entry exit points) that characters need to know straight away, as well as secondary things which can include other 'plot object/s' and 'red herrings'. Possibly followed up with a second description that highlights the plot object/s and dismisses the red herrings in the event that players miss or latch onto the wrong things.
As another thing that is possibly useful for GM writing, is a list of suitably descriptive words that will evoke an adventurous atmosphere. Instead of creeps, why not slinks? Instead of tall, why not soaring? Instead of dark what about inky or sinister? If you want to encourage GM creative writing, having a list of adjectives, verbs and adverbs to inspire as a starting point might not be a bad thing, as well as some examples taken from literature or created by other MW GMs so people can see what sort of stuff is good descriptive writing. I learn best by seeing and imitating.
There are two problems that I have with the list of "adventurous adjectives" though.
1) sifting through the dictionary and thesaurus to create a list of cool words is a lot of work, especially when i can just link dictionary and thesaurus .com and include rhymzone .com for those special rhyming moments we have as GMs...
2) words evoke different imagery and ideas for everyone. Getting a list of "cool words" that any two people would agree on, especially 2 writers will be an impossible task.
As such I think it's best to give an example or two as you did and then list those resources.