This is something that I always get mixed up with even though I've been practicing the Craft formally for about 4 years. So here's a chart for everyone. Of course, in different traditions there's bound to be different ways of doing this. This is one of the most common ways. Some traditions don't use a different invoking and banishing pentagram for each element. These traditions would have only one way of doing so. In my tradition we use the fire invoking pentagram for all invocations and the banishing earth pentagram for all banishings. We use the technique based on movement -- it's not based on elements.
When invoking, visualize blue flames coming from the tip of your wand, athame, sword, or from your fingers. When banishing, visualize the flames going back to where they came from.