What is the best way to get cartoon ideas?

I have made an extensive study of this and have tried a few techniques.
In general, I have found that there are a number of approaches to creating a
gag. Here are some suggestions based on ideas from a number of other
  cartoonists. For more ideas on writing gag cartoons, read "the Cartoonist's
Workbook" by Robin Hall. In my opinion, it is one of the best books on the
subject and you will learn many gag writing techniques. Another good source is
cartoonist Randy Glasbergen. He has written a number of excellent books on the
subject including "How to be a successful cartoonist" among
others.

First, realize that it is NOT easy. Maybe for some, creating a funny
cartoon is as easy as sleeping on the couch, but for most of us, it is tough.
One consolation is that it does get a bit easier at times. I think the brain
become used to thinking funny and starts getting into that mode sooner. Of
course, that does not mean the cartoons get better. It may still take ten or
fifteen attempts before you get that gem.

Here they are. I will have more in future posts.

Create three columns and label them People, Places, and Things. Under
each column, list appropriate items. For the People column, you might have
cowboys, space aliens, tourists, etc. Under Places, you could have Arizona,
Munich, moon, Canada, and so on. Do the same for Things by listing clocks,
radios, computer, and steak fries.

After you have an extensive list, combine one item from each column. Do
not be logical about this. Group space aliens with Canada and clock radios. By
making these unlikely combinations, you get your brain thinking a bit nutty and
soon, you will begin to see a gag peeking out around the edge of your
notepad.

The next thing to do is carry a small notebook around with a pen. You
want to be ready to capture an idea whenever it hits you. As unlikely as it
seems, there are times when a gag will punch you in the nose or at least give
you a nudge. Don't rely on memory to record it - do it right away. Just tell the
other members of your staff meeting to excuse you for a moment as you write down
that funny thought. They'll understand.

It is also a good idea to practice thinking funny about a specific
topic. For example, you might want to do some construction cartoons or develop
some gags for realtors. Learning how to create gags for a specific topic will
help you create a batch of cartoons for a specific publication. It is a good
marketing tool.

Last, but certainly not the least, is to keep practicing. Set a goal of
writing a set number of gags a day or week - and stick to it. By forcing
yourself to be funny, you will learn how to turn it on when you need it and that
is what separates the adults from the kids.