Alien StarSwarm is from his later years (1990). He's still humorous, but not at the same intensity as his early years. But it has sharp potential. The set up is that young adults are the captains of starships. The sets up an effective jab at Orson Scott Card's Ender's Game or maybe at the military in general. So a good question ask about your jokes: Does this serve a larger purpose?
Descriptions can make effective humor, especially in contrast. If you have a robot, maybe you'd expect a somber if dynamic, possibly bombastically enthusiastic comparison, as is prone in the sense-of-wonder field. Instead we get:
"The spider robot waved two tentacles.... He had a body mass about the size and shape of an aluminum beer keg."Finally, names themselves can be funny. The enemy is a group of aliens called the Balderdash--not just because it means "senseless talk or writing" but the sounds themselves are funny. But Sheckley doesn't stop here. He plays on their name a few times over, heightening not just humor but also meaning, which makes for some of the novella's best humor.