Yorkie's ears are usually tipped. I use a 10 or a 15 blade on a pair of clippers and run them on the top 1/4th of the ear. Then I use a short straight shear to bring them to a point and a pair of thinners to blend the ear length into the head.
HOWEVER~~!! If you don't know what you're doing, the rules of ear handling in grooming, or your dog isn't very well mannered on the groom table you run the risk of seriously hurting your dog so if you're not sure... don't do it. Do the rest of the clip then stop by a groomer to ask them to tip the ears for you.