It's not just Ivy League colleges that will look at your long-term scholastic achievements and grades, but they will closely scrutinize any lapsed grades from your entire school career. You have to perform at a consistently high level over a number of years if you are to win successful admission to an Ivy League establishment. The colleges will pay particular attention to your grades during high school as well as your SAT scores; nearly all students that gain Ivy League admission have very high standardized test scores, so make sure you're one of them. Bear in mind that, while it is the rest of your application that will set you apart from the crowd, you will not have a good chance of success if your SAT scores are low.
Ivy League college admissions office will look beyond your grades and SAT scores to your extra-curricular activities; they will look for examples of you as a leader and an organizer. List details of any leadership roles you have held, such as captaincies of any sports teams, or organizing roles, such as the editor of your high school newspaper. Ivy League colleges are also keen on looking at candidates that have taken up positions in the school council -- for example, those who have been class president.
Your college application essay is often your first point of contact with an Ivy League institution. Directly answer any questions that are posed on the application, taking a clear approach to emphasizing how you, as an individual, stand out from the rest of the applicants. Your grades speak for themselves, so there's no advantage to repeating your academic achievements; focus on the positive aspects of your life, rather than taking a negative or cynical approach. For example, many applications ask you to describe an occasion where you overcame adversity or handled a difficult situation, so always remain upbeat when detailing this experience. Finally, clear up any spelling, grammar and punctuation mistakes to make sure you don't lose any credibility for a lack of professionalism.
The adage "been there, done that" is relevant here. Seek out advice from an Ivy League alumnus on how to write your college application essay and prepare for the interview. If you don't know any Ivy Leaguers, search career profile websites such as linkedin.com and try and find a local link to an alumnus and contact them directly. There is no need for false pretense when contacting alumni, just be open and honest about why you are getting in touch with them, and they are likely to help you out. Write a formal letter to state your case rather than sending an email, which can be easily lost or ignored.
Nothing beats preparation before your Ivy League college interview. Techniques used by these colleges to interview their students vary from the light and informal process carried out at Dartmouth through to the intensely-pressured environment of Harvard interviews. Enter the interview with a few topics prepared in your mind, but do not learn any speeches word-for-word. Firstly, colleges look for you to use initiative, and often deliberately ask you off-the-wall questions to test how your mind works; secondly, it can be hard to make a rehearsed speech sound authentic and unique.