With emphasis
@Cry:
If you are really limited to only a few rules then you need to sit down with somebody with a clue, explain your network and your concerns and work with them to highlight your top risks. From there they can help you identify the most appropriate rules for you.
You'll need diagrams, details of applications and operating systems (including versions and patch levels), what the network is used for (web browsing, email, etc) and what your concerns are.
Re-read the last sentence in my previous post though before you go wasting your time.