Register using your Facebook account.
This increases security as it allows users to do background checks on each other. Knowing that you have a mutual friend really helps.
Set your profile properly.
Use your real name and a picture so that other users can find you!
Don't take too long to reply.
Be courteous and reply when a driver offers a ride or chats with you. You can come to an agreement on fare, time and final pickup/drop-off locations too.
Being late is often disrespectful and bothersome to fellow carpoolers. If you are running behind schedule, simply just let your driver know.
Don't forget to rate your ride.
More ratings create a more credible community. This will also help increase your chance of being offered a ride by other drivers.
Build a community.
Build a network of drivers. Don't just rely on one regular ride to compensate for sudden unavailabilities.