1.) Prepare for standardized tests
Scores on the SATs/ACTs carry significant weight in the college admissions. Take advantage of the summer holidays to prepare for these tests.
2.) Involve in extracurricular activities
Colleges love to see students with passionate and consistent involvement in productive activities that relate to their personal interests and demonstrate leadership & initiative. Being athletic, playing a musical instrument, running a foreign language club etc. are some examples.
3.) Take college level courses
Colleges like students who are high performers. Taking advanced courses indicates that you take initiative and have a high chance of graduating. There are many options like APs, MOOCs, and Coursera etc.
4.) Dedication to the community
Colleges are looking for students with philanthropic values. They prefer students who are long-term volunteers and contributors to the society. This shows your commitment to a cause and may give you a great experience to share in your essays. Find an organization where you can volunteer during school year as well as summer.
5.) Special programs or camps
Get enrolled in specialized programs for high school students. There are many options available internationally. Depending on your interests there are sports camps, education camps, arts camps, day/night camps, pre-university/pre-IB camps, leadership camps etc.
6.) Work experience
Summer internships are a great way to stand out in your application. Schools prefer students who have worked in their field of interest.