I remember when I was car-less and needed a lift, I would always, ALWAYS find someone that would want to give me a ride. I was not lucky nor resourceful, I simply made the car owner want me to carpool with him.
First look at it from the driver's point of view. Carpooling is a pain in the butt. It can further strain a busy schedule, lots of running around for nothing, lots of following up and nagging. Splitting the gas doesn't cut it, since actual fuel costs are always dollars, and nothing in proportion to the $800-1400 needed annually to keep the car (which is why the longer people own cars, the less they fret about gas costs).
So how did I make someone want me to ride with them?
1. I was generous. Often I paid for gas by myself for the WHOLE trip. Why? Because $40 in gas for a luxury limo-style door-2-door service was still better than $60+GST+PST for a stupid bus ticket. Having to wear your fatigues to lighten the load isn't fun. Nor walking around in the open with your big gun case. If I were a cop and I saw some kid with a big gun case, I'd stop him and make him show it to me.
2. I went to their home. Unless the driver offers to pick you up, don't ask them to. Make it obvious that you will show up at their place (or elsewhere) at the time they want you to. Drivers aren't stupid, and fully aware that you would prefer being picked up from your home, so asking them is cornering the driver into being uncomfortably polite.
3. I was always reachable. If the driver has a change in plans, they want to be able to call you right away, they don't have time to waste on msn or email. So leave them phone numbers of your home and your work. Give the driver your schedule. If you don't have a cell phone, borrow one from a family member.
4. Bring gifts. I always had bags of snacks and drinks. I had pringles, gatorade, and wagon wheels. You'd be surprised how much happiness $10 can buy at any grocery store. The driver probably didn't have time to eat or get snacks. And if the roadtrip was long, I would ask them what kind of McDonalds they wanted while they were fuelling up at the gas stop. Drivers can be polite and give you money to get their food, I always rushed out quick and just said they could pay me back after, and I'd just forget to ask them for any money.
Remember, all of the above tips are easier done when there are 2 or 3 people to fund the ways to please the driver. So, if you're thinking that you only need to offer $5-10 for gas costs, and still can't find someone to offer you a ride, now you have an edge to "sell yourself out".