A good place to start is by creating an effective evacuation plan for your premises. This can be a frustrating process if you've never done it before and don't know where to begin.
The best place to start is by finding plans of the building in electronic format that you can edit to your liking. Using paintbrush or any other image editing software you can crop, resize and erase parts of the image that you don't require. What you are trying to do is create an outline of the building with most of the detail removed (ie. plants, plumbing etc).
Once you have created this outline you can start adding in important features such as extinguisher locations, first aid kits, exits, muster points etc. These images can be found below and can be cut and pasted to your plan (image taken from www.buildings.com)
Here's an example of one I did for a client a while ago using their building plan. I edited out a lot of the detail and pasted in the important features.
Once you are happy with the plan, add in any important contact details such as police, fire, ambulance, local doctor etc.
When selecting a muster point, ensure that it is safe for employees to wait there whilst emergency crews arrive at the scene. For example if you are on a busy road, it might not be safe to set the muster point at the other side of the road.
Always check legislation to ensure your plan complies with requirements as they may differ from state to state.