Leather lacing is similar to sewing fabrics, but because leather is a thicker and more durable material it requires holes to be punched in it before lacing can begin. This causes the lacing to have a wider spacing than when sewing fabrics. Like with sewing, there are a variety of stitches that can be used to lace leather.
You can use a leather punch or a lacing chisel to create the holes in your leather. Make the holes wide enough that your lacing material will be able to pass through, but no wider than necessary. You can lace with waxed thread, which will use very small holes, or with leather strips, which will normally need holes 1/8th of an inch in diameter. If you are using a stitching pattern that passes your lacing material through the holes more than once, take that into account when determining the size of the holes.
Space the holes evenly along the sides of the leather, leaving very little space between the holes and the leather's edge. Create the holes on both pieces of leather that you are lacing together, and be careful to make sure the holes line up correctly. Depending on the thickness of the leather, you may be able to create the holes in both pieces with a single punch, which will increase the accuracy of how well they line up.
You can chose from several different stitches when lacing leather which will give the finished lacing different appearances and strengths. The simplest stitch to do is a running stitch. Line up the holes on the two pieces of leather, then run your lace through the first set of holes. Next run it back through the second set of holes, going the opposite direction that you went through the first holes. Then just keep repeating this pattern until you have gone through all the holes. A double running stitch will add strength to a running stitch pattern without adding much complexity. When you finish the running stitch, simply go back through all the holes in the opposite direction.
You can also use a loop stitch to lace leather. After passing the lace through each hole, bring the lace back around to the first side and go through the next hole. The lace should be going through each hole in the same direction. This pattern has a very different aesthetic than the running stitch. If you are unsure which of the stitches to use, try each of them through a few holes and see which looks better.