The development of a Life pattern is often rather amazing to watch. If you'd like to be able to do this, go to the Software section and get yourself a good program.
John Conway created the rule for Life with a very specific goal in mind. He wanted to make his simulation as lifelike as possible, and thus his laws had to meet 3 criteria:
He achieved these goals very well. You can take a simple pattern like the R-pentamino: and it will grow and change for more than 1000 generation before finally stabalizing. When finally done, it will look like this (minus a few gliders that flew away).
One feature that you will notice after playing Life for any period of time is that the same patterns tend to show up repeatedly. The still-life and low-period oscillators will be the result of just about any initial configuration. The more common still-life patterns have names.