Sprinkle a small amount of regular table salt onto a damp sponge, and rub gently inside your coffeepot. Take care not to apply too much pressure or the crystals can scratch the glass. If you find you need more cleaning power, add some white vinegar to the sponge and repeat the salt scrub.
Mix 1/4 cup of baking soda into 1 qt. of warm water; dip a scouring pad into the solution, and gently rub the inside of your coffeepot. The baking soda has both cleansing and abrasive properties, so you should see a difference quickly. Rinse the coffeepot well after cleaning it. You can also run this same solution through the coffeemaker into the coffeepot to clean out the reservoir and the lines to the coffeepot.
A more unusual method of cleaning a coffeepot is to drop two denture tablets into the full water reservoir of your coffeemaker. The foaming action helps to abrade away coffee and water deposits. Allow the denture tablets to fizz completely, and run the coffeemaker through a full cycle. Discard the water and denture formula, and run at least two more cycles with fresh water each time. Rub out the inside of the coffeepot with a sponge to remove any remaining residue, and rinse well.
Vinegar helps to dissolve deposits that enable coffee stains to stick to surfaces. Make a solution of 3 parts water and 1 part white distilled vinegar, and pour the vinegar and water into the coffeemaker's reservoir. Allow the vinegar and water to soak for a few minutes, and run a normal cycle. Repeat the vinegar and water as many times as you wish, and run a cycle with fresh water to rinse. Rub out the coffeepot with a sponge.