Practice makes perfect !!!, when I finally went full face, I worked with it out of the water for several hours, got it in winter time of course, during the 1st dive at the end of the dive, I asked my buddy who is also an instructor, that I wanted to go back down and practice a ditch and don to my spare mask. We were below the hole, and my buddy was right next to me, so went for it. the time at home certainly helped. I had more of a problem unzipping my thigh pocket than anything else. My new drysuit has velcro for the thigh pocket. But it's best to try something new with a buddy, after you practice enough to feel comfortable in trying. Needless to say, the ditch went perfect, got to my alt air source as planned w/no problems, then spend about a minute getting my spare mask out, once out tho, popped it on and cleared it w/no problems. This summer I practiced in the pool and shallow solo dives in the quarry, a ditch and don of the full mask, this encompassed using alt air while prepping the full mask to put it back on, then clearing that (easy just hit purge!). Now I am fully comfortable in case I would ever get my mask knocked off, and I will continue to practice these skill along with others when I have spare time on a dive. Never hurts, you do things until they become 2nd nature, and then you re-visit those skills to remind yourself occasionally.
you have a great idea in practicing, alot of the posts here reflect that too. Divers who think they know it all and wont learn anything else, are not realistic. You learn on every dive, sometimes it's new, sometimes it's a reminder. but you are always learning.
Congrats on your OW !