As for difficulty, so far I've found it easier to earn local scholarships rather than national ones. Talk to your high school guidance counselor to talk to him/her about scholarships.
Different scholarships look for different qualifications. Often, they're looking for a well-rounded student: high-achieving student who is involved in extra-curriculars, volunteering, and so on. Some scholarships are specific for students who have financial need in addition to being high-achieving, but not all of them are.