Making ECs stronger in a short amount of time?

<p>I'm midway through my junior year, and I don't think my ECs are that strong/interesting.</p>

<p>(For simplicity, years of participation/leadership are anticipated, so I intend to do them next year as well and keep my positions.)
Model UN - 4 years, Hoping for officer positions to exist next year. If so, it won't be hard to get one.
UNICEF club - 4 years, 3 years officer
NHS 3 years - 3 years officer
BETA club - 3 years
Debate - 2 years, hoping for officer position next year
Student council - 3 years, 1 year officer (dumb popularity contests...)</p>

<p>Also, I was on the tennis team last year, which is so easy at my school. Its a walk on team, and you don't even have to know how to play to get a letter. I intend to do it again this year. </p>

<p>Any way to make them stronger without becoming that senior who just joins every club for college apps? I'm really into social studies, history, and IR kinda stuff, so ideas related to those would be good. Also, does having a job look good?</p>