Occasionally your clothes iron will develop build-up, whether from starch or scorched fabric on the face or sole plate, or from water-sediments within the reservoir.
You will need to clean the sole plate to keep it from staining clothes, and the reservoir so that you will be able to use the steam function.
First, the sole plate: (Note: For the methods of cleaning the sole plate you will want to unplug the iron and let it cool completely.)
Dip a scouring pad (not a metal one, or you will scratch the sole plate) in soapy water and use it to scrub away the build-up. You may then use a wet paper-towel to wipe away the soap.
Some people have an aversion to soap. Make a paste from baking soda and water, use that to scrub the face of the iron. This takes a little bit of effort but works well as the previous method.
Aerosol oven cleaner
This is for particularly stubborn build-up. Some stains on the sole plate may be burned in and impossible to remove with the previously-mentioned methods. Lightly spray the sole plate and let it sit for 30 minutes, then scrub with a scouring pad.
Aerosol lubricant (like WD-40)
This is for those situations when all else has failed. Lightly spray the lubricant on the sole plate and let sit overnight. Use a scouring pad to remove build-up, then use a damp paper towel to remove remnants of the lubricant.
Cleaning the reservoir:
For this you will need to plug your iron in. Pour a quarter cup of white vinegar into the reservoir and steam until empty. Repeat as needed until the build up has been dissolved.