I've found while knitting different images with different color yarns or knit purl stitches. I used a graph to knit the bunny on one of my other instructables. It's really helpful to have it how to have it laid out for you.
As an example I'll be making a mustache on graph paper

You'll need graph paper and a pencil and if you plan to knit what ever your making or this mustache, knitting needles and yarn.

Step 1: Draw What Your Making

In a mustaches case, it has to be the same on both sides, so draw one side of it on your graph paper, draw it like your just drawing a mustache at first.

Step 2: Convert to Boxes

Now you need to convert your mustache into a boxes, like pixels. You may have to adjust it at places to make it look better

Step 3: Mirror It

Now mirror the on the other half of the stache you have now on the other side

You don't need to do this if what your making isn't the se on both sides