Once you have all your supplies together, you need to decide how you would like the finished needle felting embellishment to look. You can make it as simple as adding stripes, as shown, or add dots, shapes or any design you like.
One easy way to needle felt more complex designs is to use a cookie cutter of the size and shape you want your finished design to be as a guide for placing the wool.
No matter the design you've chosen, you want to work in smallish sections. Tear or cut a piece of roving and lay it in place to begin your design. Erring on the side of less roving is a fine idea, since you can always add more.
If you're using yarn as your needle felting material, start with one strand. For a felted shape, simply put it in place where you'd like it to be and you're ready to begin needle felting.
Remember to always place your base fabric on the needle felting brush or foam before you position the fiber where you want it to go.