The 'Rule of Life' is a very practical way of getting your life organized according to your priorities. You could say that it is just a religious name for time management which also takes into account your spiritual growth, and I would not limit its usefulness only to vocational discernment - it is a great way to get a handle on your life.  

The handiest way to do it is to take pen to paper. Take a notebook you will use just for this and stick a few tabs giving a dozen or so pages to a tab. Mark them: priorities, problems, goals, getting there. 

Under "priorities," list what is really important to you (character traits, qualities to develop, things you are going to do everyday, the things you really want to do in each area of your life). 

List also your problem areas. Your time wasters (Internet, phone, TV...), your weaknesses (such as inconstancy, impatience, vulnerable to peer-pressure, etc.), the things you are sorry you did yet keep on doing. This takes time, and it will help if you journal a little. 

Once you have done the above you will need to state your goal. If you don't have a purpose (it is amazing how many of us have only a vague goal in life) you need to think it over: What type of a person do you want to be? What do you want to get out of life?  

Now you need to make a list of the concrete things you need to do in order to achieve these goals in your daily occupations. For example, if you want to overcome laziness you are going to have to go to bed and get up at regular times, you are going to have to make your bed each day... If you want to develop a prayer-life you have to set time apart each day for prayer and devotions. If you want to know your faith you will have to take certain classes, or read certain books... The great thing about writing it down is that it makes you be very clear and concrete.  

Next you need to distribute your time, a daily routine, a weekly routine. Schedule in enough recreation.  

I can only mention some general things here, but if you have someone who knows you that you trust that, talk these things over with him in order to make this more concrete.  

As regards your spiritual life look at the goals you have set for yourself (for example: steady life of grace, openness to what God wants, etc) and then the means (for example: more frequent confession, more personal discipline, more frequent Communion, etc.), and then see how you are going to fit each on in your day and week (when confession is available, time of day I can go to Mass, the prayer I need to do each day, etc.). Your friend can help you here to see you are not trying to do too much too soon, and that you are not doing too little too late, either.  

Then look at your duties (studies, work, health, your obligations towards your parents, etc), your goals and needs and how you spread them out over your week.  

Then look at what you want to do for others (teach catechism, coach younger kids, boy-scouts, altar-servers, meals on wheels...).  

As regards your vocation, I would recommend that you gather the information you need, set time aside for a retreat, plan on visiting the places you are interested in, take care of obstacles (work to clear up your debts, for example), look into the practical implications (when the entrance date is, the application process..). It is relatively simple to set deadlines on a calendar, and post it where you can see it.  

It won't work out perfect the first time, but as you try it you will get to know yourself better and will improve. Some people have more of a knack for organization than the rest of us. If you have a friend like that get his help.  

One final, very practical point: once you make a rule of life don't file it away. Stick it where you can check it at least once a day. I suggest somewhere not too visible because if it is always there you will end up not seeing it, it will no longer register even if it's there in front of you. Try the back of the door of a closet. Set a time (usually good first thing in the morning) to check on what you have to do today, and then one (usually towards the night) to see how you did.  

You can include that in a short daily examination of conscience.