A tear can ruin the whole look of your leather jacket. Well-worn and faded leather can have a cool vintage look, but a torn jacket always looks worn out and ready for the dumpster. Even if the tear is small enough to go unnoticed, it will grow over time to the point where you won't be able to ignore it. Rather than throw your jacket away, repair it.
Cut a square of cotton cloth with a pair of scissors. The square should be as wide as the tear in the leather. Use sewing seam rippers to separate a section of thread between your jacket's lining and the leather wide enough that you will be able to reach the underneath of the tear in the leather.
Put fabric glue on one side of the cloth and place it underneath the leather tear. Use masking tape on the surface of the tear to keep the two sides of the leather together until the glue bonds the patch to the underside of the tear.
Remove the tape from the surface of the tear. Apply repair sealant from a leather repair kit onto the surface of the tear, and spread it over the surface to fill in the seam.
Place a piece of textured paper from the repair kit over the repair sealant and press down. The leather repair kit should come with different textured papers. Choose the texture that matches that of your jacket. Place a frying pan under the jacket and use a heating applicator from the kit over the paper to dry the sealant and make it bond with the leather. If the kit does not come with a heating applicator, use a hair dryer. The frying pan under the jacket will help hold the heat around the sealant and speed up the bonding process.
Remove the textured paper and let the jacket cool down. Repair the ripped seam in the lining with a sewing needle and thread.
Leather repair kits offer repair sealant in different colours as well as kits where you can mix different colour sealants to match the colour of your leather. Unless your jacket is black, it is unlikely that you will find a matching colour sealant without mixing the colours yourself.
Make sure that you follow the directions for heating the sealant. If the sealant is not heated enough it could fail to bond properly with the leather.