There is just 1 tip:
you will need a good story
There is no trick for 'one man shorts'.
How people will handle this is depending on the story and the chosen style.
But you could try to project the madness to the public:terrorize your viewers with loooong shots and boredom and then shock them with a twist
Remember: film is about showing what happens (or doesn't happen).
So how do you visualise the boredom?
How does the madness creep into his mind? (How do you show it?)
Why is he alone?
Where does the story end?
Is there a real psychological story behind it or is the movie about atmosphere?
You don't have to anwser these questions here, but you will need to know the anwsers.
The difficulty with one man shorts is relating to this 'one man'.
Interaction between humans shows a lot about a character, without this interaction the 'man' needs to show his character through action only without interacting with other individuals.
I hope this is helpfull.
Good luck!