I've never really been able to write comedy, any more than the odd moment of humour at least. This Pit is probably one of my most comical pieces, which says it all really. I hope you find humour in the bizarre... ;)
One thing that commonly suffers in micro-fiction is character description. Shorter shorter fiction will always have certain restrictions, which is why you have to work hard to evoke a sense of what you are conveying, and let the reader's imagination work hard too. With characters I often try and convey a sense of personality rather than physicality, I think that is probably the more important aspect to convey. People will often have their own, different ideas of what a character in a book will look like, but the personality is the key: it is (for the most part) what makes them who they are.
So it's probably odd that a stranger who has less than half a story and no name gets more description than most of my other characters.
"He had unruly dark hair, stubble and a tan trench coat. He looked like a TV detective."
Odder still that I describe a stereotype, and then confirm that stereotype. But it is (I hope) an instant image. Whether you picture the pulp detective from a book jacket, or a Columbo type figure, you still have a picture. The words have done their job.
This Most Unfrabjous Day and This Alien Land both go into physical descriptions. For the former it helps establish the characters, the chalk and cheese partners and the physical state of Barry, which is a mirror of is decaying mental state; in the latter the first half of the story is character (or creature) description, because that is the story...
I think one of the ways flash fiction falls into the cracks between prose and poetry is that, in a very poetic way, they are often trying to capture and evoke a single image or feeling, a snapshot of something, real or otherwise. They try and pin something down so that it can be released fluttering and free inside your mind. But flash fiction is a scene or a snapshot, something captured from something larger; for me fiction should be synonymous with story - micro-fiction is a story in miniature to me, a glimpse of narrative, one or two steps of a larger journey.
Of course there are many arguments to be had in all directions as to what exactly constitutes poetry and what constitutes prose. And what separates the two, or even if they need be separate... It is in this no man's land, this fertile wasteland, that flash-fiction falls.