I've been planning on writing about this more extensively, but basically, most of my punches are wordplay. And, how I write the wordplay is as follows:
Find the conjunctions!
Some sounds are both very common to hear in words, while simultaneously being very common, brief words in the English Language, such as in, n', or, s, etc. All you have to do is pick apart a bunch of words in this manner, until you find one that works with or without the conjunction still attached to it. Then, you just add or remove on the ends of the words to get something more complex. Easier said than done, I know.
For example:
Shaman / Sham N'
Broccoli / Brock - uh' (or) - Lee
Telomerase / Tell Em' Erase
The other one is to just say words aloud, and not think about how it is actually spelled. Just concentrate on the sounds. This, however, usually just ends up doing the same thing as the above method. You can also try to use your opponent's name, or some fragment of it (preferably at the beginning) as a conjunction, and try to think of words that contain that (which is how I came up with my Beyblade line in the GC, which is still my favorite punchline that I've ever written @
Obey).