Warning : these simple tips come from a hobbyist with no formal art/animation training or experience. Don't take them too seriously.

Moho limb/joint variations

File containing all the variations shown here : limbs.zip
Open it in Moho, select the bone setup you want to play with, then switch to animation mode.

Standard

The standard limb set up in Moho is the IK/FK (inverse/forward kinematics) limb. Just add a bone as a child of the torso/pelvis, then add another bone as a child of that one.

This gives quite a nice default limb that can be manipulated as an IK chain by manipulating the outermost bone. You can also choose the rotate manipulator and rotate the bones using forward kinematics, which can possibly give nice arcs of movement.

Multiple hand shapes can have their own bones, as a child of the outermost bone (see the tips page on multiple visibility layers, another tips page giving hand structure examples is under construction).

There are, however, drawbacks to this simple limb setup :

You cannot constrain the end of the limb to an object e.g. an arm to a prison cell bar, a leg to the ground. Moving the torso/pelvis means the hand/foot is also moved, which can lead to problems for the animator.
To a certain extent you can alleviate this by using a short 2-point spline or a bone as a marker to re-align the end of the limb each time, but this is a little tedious.
You cannot show "foreshortening" of the limb as it turns toward the viewer.
No easy squash-and-stretch

Variation on the standard

Adapted from a 3D Animation:Master setup, the three-bone joint or "soft" joint explained by Jeff Paries in his book The Animation:Master Handbook.

Here I've added a couple of bones to the default limb - a hand/foot bone and an "elbow/knee bone". The elbow/knee bone enables re-alignment of the elbow/knee points to preserve some appearance of volume. As both the hand/foot and the elbow/knee bone are children of the forearm/shin bone the forearm/shin may still be used in IK.

The hand/foot bone does not need to be used if you are using multiple hand setups as children of the forearm/shin - the main reason it has been added is to stop the elbow/knee bone from affecting the arm through IK. If you do use the hand/foot bone, it will be isolated from the IK chain (as will the elbow/knee, of course) - as this is the way I prefer it, I do not class this as a drawback. You can use this setup for arms in a number of circumstances, bearing in mind that it is lacking in squash-and-stretch, foreshortening, and constraints. As in the standard limb, it can possibly be used for nice arcs of movement through FK.

You can use this bone variation with a single, double, or triple-part joint.

Drawbacks :

Same drawbacks as above standard setup

Maestri reverse/"broken" IK

This setup (adapted from a 3D Animation:Master setup explained by George Maestri in his book Digital Character Animation) actually uses the foot or hand as the parent bone in the IK/FK chain for the limb. You can make the extremity a child of a patriarch bone, enabling you to move the whole character if required.

As in the previous setup, I have also added a knee/elbow bone (child of the thigh/bicep) to affect the apparent volume of the limb - to prevent this affecting the IK chain, I have also added a little hip/shoulder bone, although it has no other function. Again, this may be used with a single, double, or triple-part joint.

Note that I have also added a toe/finger bone as a child of the foot/hand bone. This prevents movement of the thigh/bicep or shin/forearm bones from affecting the foot/hand position through IK.

Being the parent bone of its own chain, the foot or hand remains immovably planted on the ground/object, making this a good choice for legs/feet, bearing in mind its limitations.Thus you can adjust the torso/pelvis without moving the the feet (or hands). However, you will need to reconnect the hip/shoulder joint after any movement of the torso/pelvis.

The main advantages of this setup :

Easy to set up and understand
Foot/hand remains in position when torso/pelvis is moved
Length and orientation of the limb are maintained by the software, not the animator

There are still drawbacks with this method.

The joint contacting the limb to the torso/pelvis needs to be re-aligned on each keyframe e.g. the thigh-bone needs to be re-aligned with the hip, which still remains somewhat tedious (although not as visually obvious to the viewer).
Still no foreshortening
Still no squash-and-stretch

Greenberg floating joint

This setup (adapted from a 3D Animation:Master setup explained by Steph Greenberg in Doug Kelly's book Chracter Animation In Depth) gives you foreshortening and a version of squash-and-stretch.

Both the extremity (hands/feet) and the knee/elbow joints are children of the patriarch bone. The knee/elbow and the hands/feet are totally independent or "isolated" from the motion of the torso/pelvis.

This is the most flexible of the joint setups presented here, but does require the same (or even more) re-alignment of the joint bones to maintain correct volume. It gives more possibilities to the animator at the cost of more routine work by the animator.

Again, this may be used with a single, double, or triple-part joint.

Drawbacks :

You may need to re-align many of the bones involved on each keyframe (more work for the animator)
The animator is completely responsible for maintaining the length and orientation of the limb sections.
(I am considering using this setup but also including standard IK limb bones as part of the skeleton, with no points assigned, purely to give an indication of standard unstretched/unsquashed bone length)
While the limb will squash-and-stretch, the appearance of retaining volume (i.e. adjusting the width of the limb) needs to be done manually.