I bolded the most important parts:
Start now. You will ALWAYS be too busy/distracted. What will your BA be in? Will you be at a catholic school?
Does your school have a chaplain? See if he would be willing to offer you spiritual direction.
Go to Mass every day if possible. If not, make a conscience effort to pray seriously every day. Meditate on the daily readings, and listen for God speaking to you through them. There are many resources you can find about how to cultivate a deep prayer life, if you need pointers.
Be aware of your feelings and emotions; God gave you them for a reason. How do you feel when you pray? How do you feel about the future? What is it about you’re study that interests you? How can you use it to love God more? Remember that if anything makes you anxious, it is probably not from God.
Make friends with people. Lots of people. If you are discerning Priesthood, you should be skilled in relating to other people. Join a Catholic, or Christian, group if your school has one, or start a bible study.
How would you feel about dating? Pray about it. Marriage is a vocation too. Since you’re not in seminary yet, I don’t think you should avoid dating just yet, but only you (and maybe your spiritual director) will know if it is the right move. Again, be conscience of your emotions.
Wheooo, long answer, and more than you asked for :D. Seriously, don’t put it off till you graduate. You will be sorry if you do.