First, thanks for reading the blog and congratulations on starting law school this year. It’s going to be a fun, challenging time and my most basic advice is to really enjoy it! Push yourself to try/learn new things, find subjects and activities you enjoy, and use this time to get better-connected with your wife, family, friends, and peers. Three years will absolutely fly by. 

Ok, now to (what I hope is) the more useful advice – or, the basic advice in context.

1.  Beyond your core curriculum, take classes you’re interested in. Don’t take classes you really couldn’t care less about just because you think you should or because they might be a bar exam subject. (I learned this lesson the hard way with Corporations.) Taking classes you are interested means you’re more likely to do the reading, pay attention, give the material some real thought, and just plain try harder. End result: you’ll have more fun (see basic advice above) and your grades will likely be better. One of my favorite classes at law school was Admiralty Law – yes, the law of the sea! It was completely unrelated to my current practice, but I was interested and I enjoyed spending the time to do the reading and think about what was going on in class. (And I did far better on the exam than I did in Corporations.) By the way, if you’re worried about the bar, I recommend a bar prep class after you graduate. BarBri, Piper, and others are in business (and making money) for a reason; spending the cash will be worth it – to either give you what you need to know or to build your confidence enough that you actually use the knowledge you spend all that time/money at law school to cram into your head.
2. Do more than just go to class. Certainly for the JAG Corps (and probably for many other businesses, firms, organizations, etc.), a strong applicant has more than just grades on their resume. You should get involved with your law school and/or your community. You don’t have to do everything and join every group at school, but do something. Find something you enjoy and spend a little time outside of class and studies pursuing it. This can be tough with family commitments (and a new baby) at home, but see what you can do. You’ll be able to add a little personality to your resume and will just be a more well-rounded person when this is all over. 
3. Don’t take it all too seriously. Go to class, do your homework, do some volunteer/school club time, and then make sure you spend time with your family and with your friends. Don’t talk about US v. Name That Case every time you get together with your peers at school. Make connections that are more than book-deep. Take a little time off here and there. Go out. Have a beer. Relax.
4. Stay fit. You don’t have to compete in Ironman triathlons or World’s Strongest Man competitions, but do something to stay in shape. It will help you take a little time away from the books, helps relieve stress, and will make those sleepless nights with the new baby a little easier (not easy, but easier).
5. Keep your options open. You want to join the JAG Corps now (and I think it’s a great plan), but stay tuned to other possibilities that will present themselves during your time at law school. Through a class, club, or summer internship, you may get turned on to a completely different line of work that you hadn’t considered before but is actually perfect for you. If after three years the JAG Corps is really where you want to be, you’ll know for sure and you’ll be able to tell me why.
6. Sell yourself. Ok, I wasn’t going to include this, but I think it’s important to know and to practice. I don’t mean you should be a shameless self-promoter. When you apply for jobs/internships/grants/whatever, don’t focus entirely on what you will get out of it; tell the prospective employer/etc. what you bring to the table, what you have to offer the organization. Describe your unique skills, background, perspective, ideas, etc. In the Recruiting Office here, I see hundreds of applications, and the vast majority of applicants spend their entire personal statement talking about what they expect to get out of being a Judge Advocate. It’s not necessary. I’m a Judge Advocate and so is everyone on the selection board; we know from our own experience what you’ll get out of it. What they need to know is why they should choose you, how will you make the JAG Corps better? (I usually save this bit of advice for one-on-one conversations/interviews with folks who show some genuine interest in getting into the JAG Corps (as opposed to just finding a paycheck). I offer it now because I think it’s pretty uniformly useful (see #5).)