More to consider while you're cleaning your battery terminals: If there's a lot of dirt across the top of the battery, it can act as a connector to connect the positive and negative terminals, essentially causing the battery to drain itself, so in addition to cleaning the terminals, you'll want to use an old rag wet in a solution of water and baking soda to wipe down the top of the battery. When you're done, rinse with clear water and wipe dry.
Also, after you've cleaned everything, check where the clamps on the ends of the battery cables connect to the cables. Note: Do this while the cables are NOT connected to the battery!
Sometimes, if there's been a lot of corrosion at the terminal, the cable will have corroded a bit, too, so you're not going to get the best connection. In that case, you may want to consider moving the clamp up the cable a little bit to the spot where all the wires in the cable are intact.
And finally, once you have everything re-connected, brush a bit of vaseline (or the more expensive battery terminal goop) over the terminals, clamps, and cable ends. This will dramatically slow the rate of corrosion in the future.