Many an otherwise great jacket or pair of jeans has been ruined by a faulty zipper. A tailor or gifted sewing machine user can replace your zipper for you, but if yours is a high quality all-metal set, you can easily fix your current zipper without any special tools or parts. Instructable-r Marcellahella offer this quick fix, using nothing but a pair of needle nose pliers. She mentions that if your pull or lower stop is really destroyed, you can grab a part from another item of clothing, or grab a $2.00 zipper you can hack for parts from a discount store.
Check out the full how-to at Instructables. English doesn't seem to be Marcella's first language, but the instructions are clear and the photos have all the details you need…so “sic” and all that: