To make a zipper slide easier and more smoothly, you can rub several household items directly on the zipper, such as a graphite pencil, candle wax or a bar of soap, to lubricate contact points and prevent the zipper from getting stuck. Zippers also get stuck sometimes when strands of thread or small pieces of fabric are caught anywhere in the zipping mechanism. Clearing these obstructions will also help the zipper slide easier.
Brand-new zippers usually operate smoothly because all the parts are calibrated just right. However, the zipper parts becomes worn and corroded due to constant use and washing. This causes tiny gaps in the tracks and the slider, which creates common zipper problems, such as a sticky zipper or a zipper that does not fasten the tracks together.
The most common and easiest remedy to sticky zipper is to rub a graphite pencil on the zipper's tracks while it is open. After rubbing the pencil across the zipper tracks, open and close the zipper to see if it has made the zipping action smoother and easier. This is also the same process when using candle wax or a bar of soap. Wipe off the residue once you get the zipper to move as smoothly as you want it to. Apart from these items, you can also use lip balm or a non-oil based lubricant like glass cleaner.