The truth is that freshman engineering classes are often difficult in very different ways than are upper-division engineering classes.
Here's what I mean: freshman engineering classes are usually difficult because they give you enormous volumes of busy work, or because they give you very complicated directions and grade very, very harshly for not following those directions to the letter. The actual concepts involved are not usually that difficult, but the classes are full of academic "booby traps." My first engineering class, Engineering Fundamentals I, did not actually involve any concepts more difficult than solving triangles with trigonometry, but the class was still extremely demanding because of its time pressure and grading schemes.
These kind of classes are really not intended to teach you any concepts; they're just intended to develop your study skills, and prepare you to pay very close attention to the details in your later classes. They're also good at weeding out the students who don't have the self-discipline to come to class. If you're a bright student, you can get A's in these kinds of classes with virtually no studying at all, since there are no novel concepts involved.
Later classes are difficult for an entirely different reason: they demand that you understand and effectively use advanced concepts. They don't necessarily require a lot of homework, but self-study is an absolute requirement. These kinds of classes require very good study skills.
The most important piece of advice I can ever give you about study habits is this:
Don't ever use the due date of an assigment to decide when you should begin doing it. Just reprogram yourself to consider each assignment "due" as soon as you get it. If you're given an assignment on Thursday, and it's due the following Thursday, you should ideally begin working on it the same night it was assigned. It should be done by the end of the weekend. If you let yourself fall into the delusion that you can do it all on Wednesday night, you are going to get yourself into some serious binds -- work from other classes will compete for your time -- and you will not do well in any of your classes. Begin working on the assignments as soon as you get them!
- Warren