I am 17 and planning on being an engineer. I want to study before hand to prepare for the difficult courses. What courses are particularly the most challenging in your opinion, things you struggled with?
At my school it's Statics and Electricity & Magnetism in first year. I've also heard almost unanimously from engineers I've talked to that Dynamics is a really hard course (it's the sequel to statics). C++ is very difficult for some people, but very easy for others.
Honestly, though? Don't bother preparing for the 'tough' courses. What you should be doing is making sure that you understand your high school science material fully, especially your math. Don't just learn enough to pass the test; make sure you really understand what's going on and that you can justify everything you're doing.
Trust me, I think you'll be a lot happier if you get a solid grounding in high school material than if you spread yourself out and start trying to learn university material. Besides, what are you going to do in second year when you can't do that any more? Good study habits are WAY more important than having a tiny head start on everyone else. What kills most people in first year isn't that the courses are difficult, but that they have very poor study habits from high school and they just can't handle the sheer amount of information being crammed into their brains.
We can't tell you what you will find difficult, because we are not you.
Some people struggle with the math. Others can breeze through the math but struggle with the fact that the "real world" doesn't always behave like the math says it is supposed to. (As one grizzled old engineer said to me in my first job, "When are you going to learn that this ****** machine has never read your ****** textbook...")
Just focus on your school math and science courses, and you will be as well prepared as anybody else.
Many people seem to have trouble with the introductory physics and calculus courses. Electromagnetism is a class that is often viewed as a weed-out class at my university.
At my school, there are a couple introductory engineering courses required. They are not difficult in subject matter, but they require a lot of work. I suspect they are designed to weed out the students who can't handle or are unwilling to spend the time required for upper level engineering courses.
As for preparation, take as much math and physics as you can. If you're in the US, try and take AP Calculus BC and AP Physics C. These will put you in a good position for your first year courses. (I don't know if there are similar programs outside of the US.) I would recommend not using AP credit and taking your first year math and physics courses. They usually cover more material and in more depth. They'll also form the basis for most of everything you will do during your undergrad, so you'll want to be strong in them.
Be prepared to spend a lot of time and put in a lot of work. It's challenging, but it's pretty fun.
If, when you take your first year courses, you find yourself having a hard time, remember there are a lot of resources available. Talk to your professors and attend review sessions. Some professional societies/honor societies also offer free tutoring. And of course, there's always PF!
I agree with others that the best approach is to 'just focus on your school math and science courses, and you will be as well prepared as anybody else'. I suspect you are a senior and have no more course choices for the year, so just do the best you can in your current courses. You'll be fine.
My toughest courses were fluid mechanics and convective heat transfer. Those were easy for others and no amount of prep on my part would have changed that because I wouldn't have had sufficient background for any advanced prep anyway. Looking ahead too much can be detrimetal. The summer before my first year of engineering classes (mechanical) I studied the course catalog for mandatory courses and totally feaked when I saw 'Automatic Controls'. I had no clue what it meant and had a huge panic that I'd be lost and flunk out of shool. By the time I took the class I had the background (i.e. prerequisite courses) and found the class one of the most enjoyable of the entire cirriculum.
I am not in engineering, but I know a few engineering students and can tell you what they said.
Some of them say that the introductory physics courses are the hardest. These would be physics 1 and 2(mechanics and e&m). This "may" be because they could be interpreted as "weeder" courses. This may also be because they have very minimal exposure to this kind of material and problem solving skills. Statics and dynamics are usually sophomore classes, but I hear these are as difficult if not more so than the upper level engineering courses. I think this is because the engineering school really wants to see who's cut out for the hard work ahead.
Other than the tough freshman/sophomore physics courses, I've heard the Nuclear kids talk about the difficulty of nuclear reactor physics course, and the reactor engineering course. These are junior/senior level, and judging from the grade distribution reports I have seen, I think its safe to say these are difficult. Also, I frequently hear people utter "ughhh thermodynamics!" haha.
Electricity and Magnetism was my hardest 1st year course. The entire course (from MIT) is on youtube. Mechanics (Statics/Dynamics) had a fairly high failure rate but if you practice the questions it isn't really all that difficult. My school also has an ODEs/Infinite Series class which can be difficult, but again, with practice isn't too difficult, IMO.