Zippered clothing can be annoying. Sometimes the zipper gets stuck or caught, sometimes it won't close all the way and sometimes the pull snaps or breaks and you can't get a good grip on the zipper at all. At times like these, you need to mend the pull, or more times than not, replace the entire zipper. It is not the easiest thing to do and requires a good set of pliers. Even with the right tools, it takes some strength and patience.
Look at your zipper pull and determine what is wrong with it. The only way you will realistically be able to mend it is if a small piece of it has broken off and you still have that piece in your possession. If this is the case, put a tiny bit of cyanoacrylate glue on the side of the piece that broke and put it back in place. Hold it there for about five minutes, so the glue can dry. Be careful not to get glue on the garment.
Use the pliers to snap off the remaining pieces of the pull you can't repair. Be careful only to remove the tab and not the slider, which is the part attached to the track. If you don't really care what your pull tab looks like, slip the wire from a safety pin or a paper clip though the hole in the slider to make a new pull. If you'd like a more decorative pull, slip a 50 mm (2 inch) piece of jewellery wire through the hole instead. Crease it where it sits inside the pull so you have a small piece of wire on each side. Put the two strands of wire together and string a small bead on them. Then twist or tie the wire underneath it.
Take both your zipper pull and slider off of the track and replace the entire thing if you'd like your garment to look the same as it did before. To do this, use your pliers to remove the metal stop from the bottom of the track. It will take some doing to pry it off. Once you have the stop off, push the slider all the way to the bottom of the track and take it off. Then simply slide the new one up the track. Put the stop back and squeeze it tightly with the pliers.
Trousers do not have zipper stops due to their design. To replace their sliders you have to pull out stitches in the garment. If you are not experienced at sewing, leave this job up to a tailor.