I should clarify one assumption: I assume that if you're writing to me, then you probably have some investment in being a Christian scholar--that in some way your sense of a calling to this vocation is bound up with your faith. That creates all sorts of unique challenges and opportunities, and there are, of course, a host of questions about the nature of "Christian scholarship." I'm not going to wade into those issues here.
Instead, I want to simply emphasize a very practical matter: If you are going to graduate school in order to pursue the vocation of a Christian scholar, there are some very simple but crucially important non-academic things you need to do.
First, you need to find a solid local congregation and commit to it. Resist the temptation to think you're "too busy" for church. Or "too smart" for church. You're not. And the sooner you learn that, the better. The academic life can easily become all-consuming, especially if it's laden with a sense of Christian vocation. It can too easily swallow up everything in its path and become an idol. It's way too easy to sequester yourself in a world that is, in many ways, weird and distorted. Your immersion in a local congregation will be its own sort of discipline: it will keep you tethered to the so-called "real world." And don't just be there as a cynical critic, looking down your nose at the ignoramuses around you. Despite all the knowledge you're acquiring, there are plumbers and school teachers and stay-at-home moms in that congregation that have wisdom you'll never have. Plus, if you're called to be a Christian scholar, in some sense you are called to be a servant. The local congregation is where you learn how to do that.
Second, maintain friendships outside the academy. This is especially true if you are married (and perhaps have children). While I was in my PhD program, our family was part of a small group (with folks who were not academics) that met every Friday night for a shared meal and Bible study, with little kids running around our apartment and young parents frazzled and exhausted, but all in this together. This group was, without question, an absolute lifeline for us during what can be a very difficult time. We also had dear friends who lived nearby and we fostered rituals that prevented us from spiraling inward. All of this was rooting; it took me out of myself; it regularly and persistently inserted me in a world where "my work" really wasn't all that important. And it was a godsend.
Third, if you are married, and especially if you have children, graduate education is going to be one of the single most powerful threats to your marriage. It tends to induce a degree of poverty, and economic issues are always sources of deep tension, especially in young marriages. Graduate education also has the possibility of becoming a mistress, a seductress (a mister? a seducer? if you're woman). You are going to be immersed in a world that is largely foreign and closed to your spouse--and that world will want all of you. And you need to resist--not in the typical evangelical fashion of thinking you'll just muster the willpower and wherewithal to say "no." No, what you need are systems and structures and rhythms that won't let that happen. That's what the first two points are aimed at. To them I would add one more exhortation: attach yourself to an older couple in your congregation who can be mentors, who don't operate with any myths about marriage, who know all the challenges of raising kids, and who are willing to listen. In a dream world, you might even find a Christian professor at your university who can model this, since they'll be familiar with the unique challenges of the academic life. But in any case, look for some folks who are a generation ahead of you and can be a source of wisdom and encouragement.
You are not a scholar first. (I'm talking to my younger self here.) You are called first to be a friend, a disciple, a spouse, a parent. The sooner you can learn to "situate" and relativize your scholarly vocation, the sooner you'll be able to receive it with gladness.