What is some important information I should have when studying to become a Diesel Mechanic/Technician?

Electrical!!!! anything to do with Electrical all of the trucks are going to drive by wire if you can trace circuits and find shorts and opens you will be a great asset to your company alot of the trucks have to do with computer programming so i would take a computer class if you havent already

Well here is how i did it, i went to a school called UTI in lisle, chicago did all their program (automotive, diesel and industrial )
I had good GPA and attendance, so i was elected for an MSAT ( manufacturers specific advanced training) where manufacturers pays the administration of 15 weeks of intense training only for there products then you work for one of their dealers for one or two years

Its a great opportunity i think you should think of
UTI is a great school and trusted by many manufacturers
Good luck

This is a good question, and it is really quite simple. If I were you, I would do what I did and find an entry level position at a shop. It may be a bit difficult at first and you may have to stray away from your traditional "diesel" shop and look for an automotive dealership (one that offer a diesel line, of coarse). The airport is also a good place to look into, I worked on the big equipment there and they had entry jobs with the smaller equipment for the younger techs just coming into the field. Once you find your position and gain some experience, that may help you determine a path you may want to follow. Like one of the previous comments suggested, "Electrical" 100% true, but that is also learned with time and experience and if you want to make money, there are many other aspects of the job you need to know as well.
Now start looking for education, a good school will teach you the basics, like the electrical and mechanical components. I worked at a dealership for about 1 year while I looked for a school, trust me, this will help teach you more and once you get the education it will help get you better jobs and more money quicker. I decided to go to one of the large colleges (UTI), but I believe the right community college with a basic automotive/diesel course would be just as good.
Once you are in the field, be aware of yourself. In my 15 years in the industry have taught me, stay humble, because you will never know it all and the guys who think or tell you they do, take their advice with caution. Never be afraid to ask questions or take advice, even if you believe the way you do things is better, try a different way, you may find you like the new way and believe me you will never stop asking questions. Take your time with your work and never rush, the major draw back in this industry is the expectation to finish as fast as possible or "flat rate" the job, this is how major mistakes are made, especially early in your career, trust me, you do not want to become a "hack" technician, they are the guys who still give us good techs a bad name, you will get faster with time, do what I still do and work at your own pace.
Remember, if you really want something, make goals, work hard and you will get it. I met my original goal to work on Exotic, high-end and classic special interest vehicles, If I can meet my goals, anyone can!

I Have been in the automotive, heavy vehicle, and off road equipment for about 15 years. I am currently teaching heavy vehicle technology for a school call Advance technology Institute, located in Virginia Beach. While in high school focus on classes like chemistry, physics, and general math will help in the long run. To be the best technician possible you will need to know things like fuel, different end gas emissions and several other things react to each other on a chemical level. It's not A must to be a technician but if you know the chemical process of making bio diesel for an example you will be in a better position to diagnose where the failure point is in the system because of bio diesel. I am in constant talk with several recruiters form large fleet companies like Ryder, Penske, and about a dozen others and do you want to know the main thing they ask me about a particular student? How is his attendance record. They care more about attendance then overall grade. Because they can train and mold you to the way they want the work to be performed only if you show up. Next come in the industry with the understanding that you will be constantly buying tools for the entirety of your career. I currently have about $100,000 in tools and still counting. But if you want to start learning diesels early my biggest suggestion would be to just go buy a diesel instruction manual from amazon. They have several good selections that you can start reading to gain some basic understanding. And if you read something that you do not exactly understand try and contact me on here. I would give my email address but they will not let me on this site. I will be more than happy to try and explain it a little bit better to you.