The definition according to dictionary.com
1. able to use both hands equally well: an ambidextrous surgeon.
2. unusually skillful; facile: an ambidextrous painter, familiar with all media.
For the military drill world, having ambidexterity means 1. being able to use both hands/arms to manipulate your piece of equipment for armed exhibition drill and, 2. being able to use different pieces of equipment (rifle sword/saber) equally well. For now, let’s concentrate on the first part of he definition.
If you watch exhibition drill videos on the internet, you will see, especially in the solo category, that most Drillers are right-hand dominant and their drill work reflects that. It’s natural, but when you realize it, you then need to do something about it. But how? There isn’t a “Simple Steps to Rifle XD Ambidexterity in 5 1/2 Days” program. It will take time. There are even top world-class Drillers who still need to work on their ambidextrous work- or at least designing their routine to display their ambidexterity.
Where to begin:There are fine and gross motor skills and you need to develop both. Start eating or using a computer mouse with your non-dominant hand, this will start building your fine motor skills and help you on the way to developing your gross motor skills. If you have already mastered several movements using your right hand (single hand front spins, tosses, spins starting from Right Shoulder, etc.), begin to do those same moves from the left side suing mostly your left hand and arm. Begin tosses with your left (most tosses are started with the right) and start incorporating single-hand catches. Experiment as well.
It will take some time before yo stop feeling awkward, but believe me, it will open up a whole new dimension to your drill and if you already have a good imagination on developing new variations of moves, you can continue with complete abandon, if you are new to armed drill and are seeking to create variations, this will help push you in the right direction.