Slice your orange in half, cutting through the stem end. Then, put one of your orange halves on your cutting board, cut side down. Cut your orange half through the stem end, again.
Use a knife to cut your orange in half through the stem end. Next, lay one half of your orange, flesh side down, and cut stem to stem down the middle. Keep your orange fourths secured and cut those pieces in half again.
Put your orange sideways on your cutting board so the stems are facing out, not toward you. Then, firmly hold onto your knife and cut off the navel and stem ends of your orange. Slice according to your desired thickness.