But don't be fooled by the low-key approach and fresh-faced innocence. Miller is a ballplayer, which he proved last year every time he was given a chance. And this spring he's a ballplayer bolstered by the confidence of 76 games in the Major Leagues, his dream now a reality following a rookie season in which he hit .265 with eight homers and 36 RBIs after taking over at shortstop for Brendan Ryan at midseason.
Miller is competing for that shortstop job this spring with Nick Franklin, his middle-infield compatriot who got pushed out of his second base job by the arrival of Robinson Cano. So there is nothing assured about Miller's immediate future, given new manager Lloyd McClendon's insistence that he has zero predetermination about who will win that competition.
Whoever doesn't claim the shortstop job almost certainly returns to Triple-A Tacoma, given the Mariners will prefer to let that youngster play and develop every day rather than sit on the bench in a backup role. But Miller isn't worrying about that right now.
He figures his job is to prepare himself and continue getting better. It will be somebody else's job to determine whether that's good enough for him to remain the shortstop.
Yeah, he's more comfortable this spring. He'll allow that. But only because he knows where he's going now, understands the big-league routine and isn't in awe of the fact that Felix Hernandez's locker is just across the room or that he's now shoveling tosses to Robinson Cano in infield drills.
"I think the biggest thing is just being a little more comfortable with the surroundings, the big league clubhouse and everything like that," Miller said. "But it's still the same mission. I come in here and it's still eyes wide open and I'm all ears, just trying to soak everything in from our coaches and some of the veterans and just get better. But I'm definitely a little bit more comfortable with the routine."
As for the fact he's been tossed into an open competition with Franklin, a guy he grew up playing against in high school and was teammates with on some select All-Star squads growing up not far from each other in Orlando, Fla.?
"We got a lot of time last year up the middle together, so we have a pretty good relationship," Miller said. "Honestly, we're more just working together. We're trying to get better, supporting each other and the main thing, at least how I look at it, we're competing against the other teams. But me and Franky, we're coming out here and trying to get our work in and trying to get better."
McClendon likes what he's seen so far of Miller, but isn't making any judgments yet on that competition.
"He's looked great," McClendon said. "He's moving well. His drills have been outstanding. He's swinging the bat well. Listen, he's the incumbent, but he's got to compete. Both of those guys understand that. I don't have any preconceived notions. I want them to go out and compete and may the best man win the job."
Both youngsters came to camp ready to give it their best shot. Franklin dropped a few pounds to 192 while noticeably adding muscle to his 6-foot-1 frame, looking like a youngster filling out at age 22. And Miller, 24, hit the weights hard as well and bulked his once-lanky 6-2 frame up from 193 pounds to 210.
"After last year, I kind of wanted to reflect and I realized, I'm playing against grown men, some strong guys, and it's a long year," Miller said. "I looked at myself and figured I need to get a little more physical. So I really just hit the weight room and track hard, trying to put on some good weight and get stronger.
"It feels good," he said. "I feel strong and I've just got to keep it going, keep up the work in the weight room throughout the year and keep working on my running form. That's pretty much it. I just want to be stronger and more physical."
As for that running form? Miller good-naturedly takes grief from teammates about his gangly style.
"It's all over the place," he said with a grin. "A wounded deer or baby giraffe come to mind. So hopefully I've cleaned it up a little bit."
But the truth is, he was able to show off that running style more than most last year when his aggressive hitting approach and baserunning led to 11 doubles, six triples, eight homers and five stolen bases in 306 at-bats, with a .418 slugging percentage that ranked fourth on the team behind only Raul Ibanez (.487), Kendrys Morales (.449) and Kyle Seager (.426).
While Miller clearly wasn't in the defensive class of Ryan, he played a solid shortstop and his OPS of .737 obliterated the .520 mark Ryan put up before being shipped to the Yankees late in the season.
McClendon says he just needs a shortstop who can make the routine plays and isn't worried about Web Gem highlights, using the Tigers' Jhonny Peralta as an example of a guy who gets the job done defensively and brings some offense to the table as well.
Miller doesn't have as much pop as Peralta, who has hit 20-plus homers in four of his last nine seasons in the Majors. But Miller has the speed to have filled the leadoff role a team-high 67 games last year and led all American League rookies with his six triples, and the power to put up three two-homer games, a feat not accomplished by a rookie since Chris Young of the D-backs and Ryan Braun of the Brewers did the same in 2007.
So while he may not look like a power hitter, don't tell him that.
"Actually, at least in my mind, I'm trying to go up there and drive a ball. I'm trying to do damage," he said. "And for me, I want to consistently drive it. Those three games where I had a couple homers, I believe you've got to do a lot right to really get into a ball. So I'm just trying to be consistent with that.
"Hopefully, I can drive some more balls more often. But I'm trying to do damage and drive some gaps and run a little and hopefully do it all, whatever the situation dictates."