First things first, keep your brake pads clean. Gunk on the brake pad could cause an unwanted, and unpleasant, squeak!
To clean the brake pads, use a scrub pad or file and scrape off the glazed-on gunk. If your brakes still feel ‘not quite right’ and the squeal hasn’t stopped, then you will likely need to toe-in the pads. Angle the brake pads so that the front of the brake pad makes contact with the rim first. To do so, loosen the bolt holding the pad to the brake arm, position the pad as desired and then tighten the bolt lightly making sure that the brake pad doesn’t slip out of position (as it does often). Once it sits without slipping - tighten it completely. Next, check the position against the rim. Make sure that you don't overdo the toe-in! Ideally, the rear should have about a millimeter of clearance as the front tip hits.