This a great question, and you've already got a good response.
But I'd file "deliberate practice" under the header of "good process." I've always been a believer that performance is a product of process and effort. Effort without a good process is a waste, as is a good process without effort.
I think a good process includes analysis and reflection. I used to write long SCG articles breaking down play-by-play from matches or tournament reports to illustrate different lines of play. But MTGO makes this so much easier.
Because you can go back and replay MTGO matches, I find MTGO to be the perfect testing medium for deliberate practice. I do a couple of steps. First, I'll rewatch the game in fast speed, to just get a sense for the overall flow and key decision points. Then, I'll replay the game a move at a time, to more carefully analyze my options, and to evaluate what I could have done differently. Taking notes is useful, as you can record key decision points and weigh options.
The other night, I lost a game 1 against a Workshop player after I made a big decision, and the line didn't pan out. Only after I watched the game twice, and really thought about it, did another line emerge to me that I hadn't even considered when I was playing it, because it was so counterintuitive. Upon careful analysis of what my opponent subsequently drew and what happened, I believe that counter-intuitive line would have led to victory (I won the match anyway).
But, at the same time, I try to ask and evaluate big questions like: 1) what matters in this game? 2) what is my strategic objective in this match? 3) What goal this tactic trying to serve? Those are questions that arise from the frameworks developed in my Gush book.
Too often, players play Magic and Vintage tactically. By that I mean that players simply try to make good plays in the situation, without really considering the bigger picture, and what they are driving towards. A firmer strategic understanding will help guide plays in ambiguous situations while also revealing the strengths of alternative lines.
In addition to that, whenever I'm playing one deck in preparation for a tournament, I usually keep a running list of "errors" I've made, and will review that list before matches. Examples might be: 1) Running into a Mindbreak Trap when I didn't have to, or 2) Strip Mining the wrong land, or 3) fetching the wrong basic, etc.) That list helps me discipline my play and reminds me what to avoid.
In life, I've found that I usually have to commit a mistake (like mispronouncing someone's name) up to 3 times before I remember to avoid it in the future. So creating the list helps me record and encode errors as a "deliberate practice."