This vid shows ear tipping using a peanut trimmer @ 2:52
I use blunt tipped scissors to cut the hair on the edges & use my thumb as a guide. If you're using natural light, direct sunlight will show exactly where to cut on the edges, you can see the skin & where the hair starts. As for pattern, there's really none...I just trim the top tip of the ear flap 1/3.
Trimming 1/3 or 1/4 is personal preference. If you're concerned about his hair weighing down his ear, then trim more off. For those that have folded ears, trimming the whole ear will help.