Dispositers are really just a way of looking at planets in their own sign, a stellium of planets in one sign and its ruling planet and planets in mutual reception (placed in each others sign). The ruler (dispositer) of a stellium planets in one sign would be significant in a chart reading because so many planets are disposed by it. Planets are always strengthened in their own sign, its like a double dose of the same energy. And planets that are in mutual reception have the same basic expression and therefore connect with another even if they don't form an aspect.
If you want to find out your chart dipositors, simply use the Astrodienst Site. If you have an account there, sign in and ‘click’ Free Horoscopes on the top menu, and load in your chart details, then ‘click’ on Pullen Astrology, and you will see a drop down menu that has different options. You need to click on Sign/House Dipositer Graph and this will automatically find your dispositors. The dispositors are the planets circled. It is an easy to use program that will help you find the dispositors for any chart that you are analysing.
Basically, dispositors are the ruling planets of each sign. For example, if you have Venus and Jupiter in Cancer, the Moon would dispose of those two planets, because the Moon rules the sign of Cancer. Using this method, you can easily follow a chain of dispositors around the chart until you can go no further. Some charts have a sole dispositor and this is usually a planet in its own sign. Other charts have more than one dispositor and planets that are in mutual rulership.
Read Kevin Burks Dispositor Trees for more information. Basically, we are looking at the links within the chain of dispositors (ruling planets) and understanding which planets are linked to one another according to planetary relationships.
You can think of it like internet networking, those of you who understand how website SEO works may get this analogy. For example, if you have three planets in Libra there are three back links to the Venus site. Planets in their own sign have an independent specialized network and they have a powerful placing in the planetary community. Mutual rulerships show each planet/site exchanging links. Obviously astrological analogies are not my forte, but find out your chart dispositor/s and see which planets are connecting to one another.
Here is an example below:
Britney Spears Horoscope has Venus and Saturn as her dispositors, Venus is in Capricorn and Saturn is in Libra and so there is a connection between the two through mutual reception and there are no planets in their own sign. Natally, she also has Venus and Saturn in square.