I suppose, then, that the most utility could be gained by donating time to local projects in your area of interest -- tutoring kids, red cross, what have you, and money to global projects. It doesn't take a lot of expertise to send $10 to starving kids in Africa, or what have you. You decide that Sub-Saharan Africa is a place where your money will probably go a lot farther than most other places, you google around for some charities, then do a little background research, and send in your money.

But with donating time, where you're doing something physically, you're going to generate a lot more utility by doing something you already know something about than by something you'd have to learn from scratch.