Darlene,
When you look at a good bonsai forest, you will notice a harmony that makes the forest pleasing to the eye. There have been some good tips posted here already.
Here are mine:
The tallest tree should be the thickest trunk. The second tallest, the second thickest. The third tallest... Well, you get the idea. No two tree should be the same height or thickness.
Placement of trees number 1,2, and 3 are very important. They should be arranged in an unequal sided triangle. The distances between trees is very important. A poor forest will have all the trees appear to be about the same distance apart. Very unnatural. A well done forest will have no trees an equal distance apart. Some trees should be very close together.
If the largest tree is placed near the front of the pot, you will be building what is called "a near view" forest. Our minds place the tallest tree in the middle of the forest. So, if the tallest tree is in the front, it's as if we are standing in the middle of the forest, looking at the Mother tree.
As opposed to: a "far view" forest. This is where the tallest tree is placed near the back of the pot. It would appear that we are standing at some distance from the forest, and looking at it from afar, and the Mother tree is well inside the forest.
Now... You want to build a shohin forest...
Uh, let's not try that as our first forest. You can still use the pot you have, but don't restrict yourself to a finished height of 8 inches. Just too hard to do, especially since you are rather new to bonsai. If you want a true shohin multi trunk composition, I think you would have better success with a clump style.
Clump style are not really considered "forests" even if they are developed from individual trees.