I use double sided basting tape to hold seams when sewing leather. It comes on a roll & is available in sizes from 1/8 inch wide to 1 inch wide. The 1/4 inch size is what most use. It has paper on one or both sides you peel off, depending on the brand. There are many brands. It is left in & hidden in the seams. Professional leather sewers use this. You can find it on Tandy Leather, Wawak, Sailrite, Amazon & many other sites.
To prevent drag place a piece of thin paper under the leather & sew right thru it, then rip the paper off. Those junk mail fliers work well & are free. You can use tissue paper or even computer paper (last choice). The thicker the paper the harder it will be to rip off without causing pull to the stitches.
If you are top stitching always tape the seams back & hammer the seam to flatten it before sewing.
Leather has stretch, so note how you cut it.
Back stitching is not always a good thing when sewing leather, so instead tie/double knot off the thread at the end of the seam leaving a tail.
Use a Teflon foot or a leather rolling foot or a leather walking foot. I use a walking foot.