A problem a lot of people suffer from is lag. The most simple of models can be ruined by bad framerates and there are simple ways of fixing this. A smooth running model=a happier you. Laggy model=bad experience=unhappy you.
The first thing to do is make sure there are as few groups inside your main body as possible. For instance, if you're making a car, don't put the doors, mirrors, etc. as different groups if they're going to stick on the vehicle.
One method to reduce lag is to group all the solid objects (not joints or lines) into one group from within the group they are already in. Example: you made a car and inside the main body group there are 2 motors, 2 servos and 14 boxes. Open this group up and group the 14 boxes together but not the motors and servos. This will reduce lag a small amount.
Another thing that holds down a model's potential is the view settings. While they increase realism, shadows, edges, profiles, and textures also increase lagginess. Turn off shadows, edges, profiles, and textures to further reduce lag on a SketchyPhysics model. In shadow settings, you can change the shading to shade with the sun. This can create a slight shadow effect, and may look better than normal shading, but this will not slow down the simulation.
Does That Need To Be There?
Many simple models are plagued by edges that were created inside the model. Many of these edges can be deleted without affecting the look of the model; these unneeded edges are only more things for the simulation to move. Sure, it's normally the tiniest bit of lag caused by each edge. However, with multiple edges the amount of lag adds up, so delete the unneeded edges.