After you've done the best job you can preparing new material and practicing, try it out on friends and small groups. Don't tell your friends you are testing. Just plunge into the joke or story and see if they laugh or give you the kind of response you expect. You must learn to distinguish polite and real laughter on your humorous material. On your straight material you must be able to read a genuinely enthusiastic response compared to the "I'm-being-nice" enthusiastic response. Your study of audience body language will help you with this. If you are the boss, don't try things out on your subordinates. Try them out on your peers. Your subordinates may feel obligated to laugh or give you favorable opinions.
The best test for humorous material is to deliver it to the company sourpuss. If he or she laughs, you know you've got a winner. Also, be careful to recognize that some people laugh at anything. Don't let them convince you you've got a good joke or story until it's been tested on many different people. While you are in the testing phase, try out different deliveries. Only change one element of the joke or story at a time and watch closely the reactions you get. If you make too many changes at one time, you will never know which change was the one that got the better response.