The million bucks question is how to reduce consumption, well most of the world's oil is used for transportation so that will be a great place to start. Even if you choose to neglect the huge impact that green house gases have in our enviroment and how we are changing life in our planet for the worse look at it from an economic perspective and how much it impacts your pocket. Here is my personal story and how I concluded ridesharing was the best thing I could do for my finances and the environment:
I commute every week between Orlando , FL and Tallahassee, FL about 270 miles each way and on average I spend about $43.50 per trip in gas, by looking at the numbers I rideshared last year and dividing it by all the number of trips I took I saved about $12.50 so I was able to reduce my gas expenses by about a quarter (I estimate my overall ridesharing allowed me a cost reduction on my gas expenses of about $1,300 a year), another great benefit is the reduction on carbon foot print, for every person that rideshares with me we are keeping about .2 metric tons of CO2 from going in the atmosphere per each one way trip (by comparison of having two cars on the road instead of just one).
But ridesharing is not only for long trip commutes, short trip commutes are also feasible for ridesharing, your own neighbors, friends and coworkers can also be interested on sharing the ride with you; you save money on gas and wear and tear on your cars if you split the drive.
Below is a link for an article about ridesharing from the New York Times that I had the opportunity to contribute for: