Ten months old is part of the Great Age of Exploration. Most kids have learned to maneuver across the room and they want to handle and examine (and often mouth) most everything they find. So the first step is to create a good environment for this. Remove as many things as possible that he shouldn't mess with and strategically place cool things for him to explore.

Still, kids do need to learn the word "no." You want to reserve "no" for only a few things at that age--activities that might hurt the baby or others or objects that he might destroy. A simple "no" followed by "no touch," then moving him or the object, is usually enough. If the room has a lot of items that can't be moved, then a portable play yard is a good idea--a place where he can handle anything he finds. But again he should have new things to discover every day.

The word "gentle" is also a great one to teach. Model it for him when he is a bit too rough. Say "gentle" softly and then show him how to do what he was doing in a more pleasant way. Around other children, if he hits or bites, it's time to say "no" firmly.