The last key element I'll discuss to help you add humor is Universal truth: a manner of discussing a well known fact, but in an abstract way.
These usually begin with something like, “Did you ever notice…?” or “If…then what?” Consider George Carlin’s “If crime fighters fight crime and fire fighters fight fire, what do freedom fighters fight?” or “Did you ever notice that anyone driving slower than you is an idiot but anyone going faster than you is a maniac?”
The protagonist in Juno is a font of universal truths. When a prospective adoptive mom advises, “Your parents are probably wondering where you are,” Juno blithely replies, “Nah... I mean, I'm already pregnant, so what other kind of shenanigans could I get into?” Good point.
Later this week, we'll discuss how to use your new-found humor skills!