The first rule is to find common ground. The broader the appeal of your subject matter, the more likely people will have experienced your points of reference and the more successful your jokes will be.
For example; a lot of comedians use the Star Wars products as their source material. For any of their jokes to work on this topic, you have to have experienced these products. Now, I have only experienced one film (which I found boring – there, yes, I’ve said it!) and so none of their jokes make me laugh – who are they talking about? Usually there isn’t even a visual gag within their Star Wars routine which I can appreciate without needing the cultural reference. By narrowing your cultural reference you lose more of your audience.
One of the best exponents of using this rule is Peter Kay. Not only does he use subject matter which is familiar to the demographic sample of your typical comedy audience (pretty much the same as a cinema audience) but it is familiar to practically any demographic in the country. How many of us have been to a fair or a wedding? Even if you are not familiar with these experiences, there is enough visual humour in his performance to make the cultural reference irrelevant.
The best way to adhere to this rule is to monitor your own routine then, assuming you aren’t an astronaut or something, most of what you do will be familiar to everyone else.
For example; if you work, you probably travel to work either by public transport or by car. The next trick is to observe what you do and what everyone else does on that journey. Do this dispassionately. Look for inconsistencies, oddities and patterns. make a note of them. If you don’t write them down you will forget (you will, trust me).
Once you have gone through your entire routine for a week you should have enough notes to make a start. Pick a subject then look at the experience from a different angle. Some work is involved here and you may need to resort to creative thinking techniques such as the Lotus Blossom technique. Any decent book on creative thinking will have various exercises for you to use.
The trick here is, to adopt a different perspective. You don’t have to agree with the perspective, just adopt it and see where it takes you. Most people will have an accepted opinion about something, so if you can show the contrary or demonstrate the stupidity of such a view, humour will arise.
For example; in the days before I had a dishwasher, I would wash up by hand in a bowl in the sink. Quite often the empty bowl would be hooked onto the protruding metal nipple that anchored the chain of the plug. As the bowl filled up with water the plastic on the edge of the bowl would eventually give way and the bowl would suddenly drop an inch or so into the sink causing the water in the bowl to splash up and soak me with dirty water. This was never a gag of mine but I remember complaining to a friend about the frequency of the occurrence. As I told them the story they found it hilarious. Afterwards, I pondered on why they found it funny and the reason, I decided, was because it was so insignificant. The listener had obviously done this themselves and thought nothing of it, precisely because it was so trivial. In effect, they had no opinion about it. By complaining vociferously therefore, I had elevated it to a major issue and it was this absurdity that forced the humour.
Rhod Gilbert has a routine about a torch with a million candle power. Most people just accept the claim on the box but Rhod takes it literally and plays around with the concept – what if it only had 900,000 candle power, is that inadequate? etc.
Note also that with the increase in dishwasher sales, my story about the washing up bowl becomes less familiar to people. Eventually, if I tried to tell it, it wouldn’t make any sense to those people who had only ever experienced a dishwasher.
Next, extrapolate. By that I mean play around with it, apply whatever modification you can think of. Any modification is usually preceded with a ‘what if..?‘ question – ‘what if I exaggerate this incident, what if I take away the people, what if this principle was applied to a similar, unconnected social custom etc. Thus, even my comment about someone not being an astronaut could be utilised; what if you were an astronaut going to work, how would things be different?
By the way, if you’re an entrepreneur looking for a gap in the market, this approach will work for business as well.