Have a really good community service record and an above average GPA (At least a 3.5+) are two things I could think of right off the bat.

Should I do lots of extracurricular activities or focus more on small jobs like babysitting and dog walking?

It's good to have job experience and a little money on the side. Both are great, but small jobs aren't really going to make a big impact in comparison to extracurricular activities. Joining clubs like the FFA will definitely help you get into a well known college known for agriculture, for example. There's also activities like joining your school's sports teams will help out.