M.W.
Motor skills are easy...if it's fine motor skills you are trying to hone in on try have him play with legos (the small ones) or blocks. Using a smaller type toy really defines fine motor skills because it makes them use only one or two fingers and their hand-eye coordination. You can also give him something like dry cheerios to eat as a snack. Large motor skills are more like playing kickball or catch with a larger ball...which makes him use his bigger muscles.
Now social skills is a whole different department. I would like to know this myself. My daughter is 15 and I put her in all kinds of sports, dance classes, etc...and she still lacks social skills. I think she learned that from me. A psyciatrist friend of mine says that children learn their "social skills" within the first 2 years of their lives. And yes...that was me the first 2 years of her life. Good Luck!!