A lot of the shaving process is done through muscle memory, so once you learn to do it, you won't soon forget how; just like riding a bike. My advice is that you do what you are comfortable with and then slowly push the boundaries. If you start to feel uncomfortable, stop and finish your shave with your DE. Just make sure you try again the next day; don't want two years.

Keep working on shaving with the grain WTG (generally top to bottom) until you are comfortable. Then try shaving either against the grain ATG or or across the grain XTG until you are comfortable. If you are not comfortable using your non-dominate hand, then shave with your dominate hand. However, if you can learn to shave with both hands, you will find that shaving some parts of your face in certain directions becomes easier with the non-dominant hand. For example, when shaving WTG, I use the hand corresponding to the side of the face. However, found that shaving ATG is much easier when shaving cross-handed; that is, shaving the right side of the face with the left hand and vice versa. But do whatever works for you.