There are a lot of ways to optimize 3D models for games, and this applies to any 3D software. I currently use Blender, these practices are very universal. Normally the approach I take is to manually retopologize the models into a lower poly version, then I would bake my high poly model onto my low poly model to retain the quality without having all of the polys.
When you're getting into retopologizing, you'll find that there are many methods to do this and techniques. Some people will use free hand tools that allow you to draw edges to form faces above your high poly model and create the new topology on the surface, while others will create vertices, extrude out edges, ect... on the surface and make clean quads. Keep in mind how your topology is set up because of animation. There are best practices for things like faces, ect...
Some software packages have auto tools that do this for you, and I frankly will only use this on stuff that I don't have to animate, or it's an object that I can get away regardless of how the topology is setup. When you do it manually you have more control.
YouTube will have a lot of videos for 3DS Max, so check them out:
No matter what tool or method you use, your main objective is to lower your poly count to (x) range, and retain good topology to assist with better animation and UV unwrapping.