I live in the Netherlands. However, I'm hoping to go to an Ivy League school in the US. Will it be harder for me to get in than it is for US citizens? What should I do to improve my chances?
It is typically more difficult for international students than it is for domestic students to get into highly selective US colleges. For example, in 2012 MIT had an 8.9 percent acceptance rate overall but only a 3 percent acceptance rate for international students (MIT isn't an Ivy League, but it's the same caliber of school). As the number of international applicants to these competitive colleges has increased, acceptance rates have dropped down to extremely low levels.
To improve your chances of acceptance, you should make sure you have perfect or near-perfect scores on standardized tests with grades to match. It's also important that you've done extracurricular activities or won awards that demonstrate your passion for a particular subject or non-academic pursuit. Try to stand out in any way that you can.
You should also check which schools have need-blind admissions policies for international students. Cornell, Harvard, MIT, Princeton, and Yale are need-blind, while Brown, Columbia, Dartmouth, UPENN, and Stanford are not. If you think you'll need financial aid for college, the need-blind schools are a better bet (they won't be influenced by your ability to pay in their admissions decisions).