Don't breeze through your Activity List!
A successful college applicant takes every available opportunity to highlight a different part of themselves. If your personal statement emphasizes your experiences as an athlete, then use the Activities section and supplemental essays to showcase your skill in fixing bicycles or your secret hobby of writing haikus.
Few know it, but your Activities section can be extremely valuable in showing the reader who you are.
There is A LOT to say about how to maximize this part of the Common App, but here are just a few basic tips:
Use strong, active (and colorful) verbs.
Don't repeat any info or use unnecessary adjectives.
Highlight both tangible ("raised $3000") and intangible ("built a team from scratch") qualities and accomplishments.
Take whatever info you can from the 150-character Description slot and put it in the Position slot. That will give you more space to elaborate in the Description. See my example below.
Position: Casual employee in family's store.
Description: Worked as a weekend employee in the family store; oversaw shelf stocking and basic accounting; communicated with customers on a regular basis. (142 characters)
Position: Weekend employee in family's store
Description: Mastered the tasks of a cashier; gained inventory and accounting skills; memorized hundreds of customer names; sampled olives and dates for freshness. (150 characters)
Notice how the very last item in this list was totally intangible and possibly even extraneous information. It's not though. Why? Because in giving specific details about your experience, the reader gains a clearer picture of you doing that activity, thus you're SEEN more clearly. The last thing I'll say is that it's never a bad idea to scatter some notes of levity in your Common App. As long as you're not flippant, the admissions officers will see that you're a fun-loving person in addition to being a serious student and that counts for more than you think. :)