Understanding your natal chart, or that of another, can be simplified by a straightforward and fun exercise: assigning roles to each personal planet (the Sun, Moon, Mercury, Venus, and Mars) and imagining exactly how these individual "players" might get along—inside us!
In a general sense, we can think of our Sun sign as our internal Adult. The Sun will listen to all of the other planets' input, but the Sun is the boss—the one who screens the action. The Sun will send out different planets on different missions. For example, Mercury when it is time for expression, Venus on a date, Mars when action needs to be taken. However, the Sun is a person's internal parent or adult, and few things get past him/her.
The Moon is our internal child. The Moon represents our feelings, often those that are difficult to put into words. When we are feeling and thinking one thing, and we are asked what is on our mind, more often than not, our Sun (adult) screens these feelings so that what comes out of our mouth is not quite the true emotions we have been feeling. Those difficult-to-express emotions and thoughts are our Moon, and what we let out of our systems is more often than not screened and refined by our Sun. How we express ourselves (the style in which we communicate), however, is ruled by our Mercury. Mercury does the talking and rules our more impersonal thought processes.
Venus can be seen as a more refined Moon. Venus expresses what makes us feel good, and is inspired when we are in partnership and romantic situations.
Mars represents action. Our first active impulse is ruled by Mars. What fires us up, what gets us out of bed, and what lights our fire—these fall in the domain of Mars. Mars represents impulse and embodies our instinct for survival—the "fight or flight" instinct.