The good shape of the microscope condenser lens is really critical to being able to see a specimen properly. I remember when I was first starting out at university and we were each assigned a microscope, for the first class I just couldn't see anything with it and thought I was somehow really bad at this, even though I did well enough during high school.
Eventually, I asked my professor about it and she came over and had a look herself. It turns out that some other student had got dirt all over the condenser lens somehow and that's why I couldn't find anything with the microscope. Once we switched to another one, I could suddenly see clearly!
Definitely something to check if you're having trouble with a microscope.