While it is important to focus on classes in your specific field of study, it's also important to be well rounded in all areas. Colleges want to see that you are taking courses in all areas, not just one. This is also helpful in case you decide to switch majors, especially because very few people already know their college major when they are picking out high school classes. For example, you shouldn't quit taking math as soon as you have enough credits in it to graduate just because you don't like math (even if you are planning on being an English major). Usually it's best to take some form of English, math, science, and history all four years of high school if you can.

And of course colleges will be looking at the intensity of the classes as well!

One of the most important things to consider with regards to your classes is the importance of taking classes that are higher level. Many high schools offer honors courses or AP classes, and good performance in these classes helps admissions officers decide whether you challenged yourself enough in high school. Secondly, while taking classes that focus on a probable field of study or interest helps, keep in mind that you are not expected to know what your major is yet coming out of high school. Finally, keep your courseload challenging and steady throughout high school -- consistency is key: admissions officers don't want to see a senior courseload that shows you are thinking of cruising through your last year of school.
One final note: while it's important to challenge yourself with tougher courses, I wouldn't recommend overstretching yourself to the point where your GPA will suffer. It is better to have a 3.8 and 2 AP courses a year than taking 5 APs every year and have a 2.8.

Does your school allow you to take a lot of electives? If it's possible, take a few electives in an area that interests you and do really well in them. If you show in your application that these areas are interesting to you, and then the school sees your success in them, they'll know you do really well in areas of interest. It also shows that you can take on some academic independence -- the ability to create your own coherent and interesting curriculum.

I hope this helps!!