If your school offers AP Economics, take it. Take AP Calculus. Beyond that, as a high school student, there’s no more "proficiency " expected.
Because economics is applied to real world issues, most jobs or internships could be relevant, whether working in the local supermarket or farmstead to interning with government. You just need to be thoughtful and observant while doing them.
Get a job at the Gap folding sweaters; talk to your co-workers. Get a job as a lifeguard at the YMCA pool- talk to your co-workers and the members. Get a job as a cashier at a supermarket.
There is no better way to understand economics than life experience. Economists deal with questions like “does raising the minimum wage help or hurt low income families” or “does increasing certification requirements in certain professions cause labor shortages, or does it increase the quality of job candidates”. Big question- Does increasing taxes on cigarettes mean that fewer people smoke, or does it just mean that smokers buy less nutritious food items so they can continue to pay for cigarettes.
You will have a more erudite point of view-- before being able to do the large scale regressions of giant datasets that economists deal with- by having some real world experience.
These appear to be rankings by publications (from research). However, as is commonly pointed out by LAC advocates around these forums, research and publications do not tell the full story about the quality of undergraduate education in the subject. For economics, a prospective undergraduate student may want to consider curriculum differences in the following areas:
Math intensity: the most math intensive economics programs use math beyond single variable calculus (e.g. multivariable calculus and/or linear algebra) in intermediate economics and econometrics courses. Moderately math intensive economics programs use single variable calculus, while less math intensive economics programs use no calculus. Pre-PhD students should favor more math-intensive programs.
Upper level electives: there are various subareas which a student may be interested in. Some departments emphasize more “business pre-professional” subjects, while others focus on other subjects.