I would like to add something... Life in You is spot on!
Can I expand? I think there are a few factors that help you come to know if you have met the right person. We can not just trust our feelings, because well that is silly, you all know that feelings can lie, they can decieve us! But feelings do play a part in knowing. I think that you and her will both know if you are right for each other when you get to know each other really well and those feelings of love increase over a long period of time, a year is a good period, but that ain't a rule. I think that first you need to be friends. This person must be your best friend. You must see this person as someone you know you can spend the rest of your life with, you must share the same vision for your lives. I have seen people get married and then divorced and the main factor behind the divorce was that they had conflicting visions for their family life, that ain't good. Obviously sacrifice can be a part, but I don't wanna get into that! Just a side note, do not enter marriage if you think escape from it is an option, that is a big "no no". I have met many couples who entered marriage with the thought that if it don't work out they can get divorced, big mistake because they usually end up getting divorced.
Okay lets sum up what I just said! Number one, feelings get stronger. Number two, you share a similar vision for life, especially family life. Number three, you are best friends. Number four, you don't even think about divorce, an escape route, if you are, you don't even think about getting married!
What else? I think it is really important that those people in authority over your life should agree that you should get married. That would include your parents, Pastor and those who know you both the most! Also, you should be as free as possible from any baggage you may have. Now the later is a hard thing, and Desper84unity touched on this. I don't believe you need to seek the help of a professional Christian Psychologist to get straight, but that can help you. I do believe however that you are not ready to get married until you have sorted out certain problems in your life. That is where and how the church can help in this, along with your own personal study. I have said this before, but marriage is a magnifying glass. If you enter marriage with problems, they will normally only increase while in marriage. (The flipside is that your good values will shine brighter in marriage also!) I am not saying you have to be perfect to get married or none of us will ever get married, but there are some things that need to be worked out before you get married. I will list them briefly and then I will shut up!
1. Finances, get them sorted before marriage or you will both get into debt. Even if the other person is amazing at personal finance, you will still mess the equation!
2. Sexual sin/list/purity. Just because you will be married, don't solve the problem. Get sexually pure before getting married. There are loads of good books on this available. For the guys, best book is "Every young man's battle" by Stephen Arterburn, Fred Stoeker and Mike Yorkey. There are also some good books out for the ladies too, I have just not read any of them!
3. Anger, get a grip of it or watch yourself explode in marriage!
There are others but this is all I can think of at the moment! Hope this helps!