Walk - Ponies can't be expected to high step constantly, so normal walking is perfectly acceptable.
Trot - A quick jog, with a bounce in the step. Be sure that it is a confident movement.
Canter - Fast trot.
Gallop - There are two different styles I've heard of, so I'll list both and you can decide which one works best for you.
- Full out run. Not recommended for long periods of time.
- As we learned as children (in the US). Stepping forward with one foot and then bringing the other to meet it, with a bit of a bounce in the step, the same foot always leading. This one also seems to take more skill to accomplish gracefully, but is more true to the real style of a horses gallop.
Skip - "Step, hop, step, hop." Most of us (in the US) probably learned this in kindergarten. Knees should be brought up to waist height for this move, since it is more of an upward motion than a forward motion (though it is still both).
Both of these modifiers can be used for a walk. The high step can be used for trot as well, depending on the skill of the pony.
High Step - Knee comes up to form a 90° angle. Thigh should be parallel to the ground.
Parade Step - Same as a high steph but leg is extended to a 135° angle to lengthen the step. Note: While this is called a Parade Step, it is not necessarily used for parades.