Check front wheel bearing adjustment. There should be no side movement of the wheel. Lift the bike and rotate the wheel. Bumps on the wheel may cause the wheel to appear to be out of true. A broken spoke will often make the wheel look worse than it is.
Back wheels are especially prone to going off true as they carry most of the load.
Check front brake pads. Make sure the entire length of the brake pad comes in contact with the rim. The pad must not hang below the lower edge of the rim and must not touch the tire. Clean pad with sand paper to remove glaze. Check headset adjustment.