Using the right needle will make sewing easy and more successful.
Needles should be as small in diameter as possible, have a blunt point, and have an eye no larger than the shaft of the needle. If the sewing needle is much bigger than the thread used, it will make a hole that the sewing thread cannot fill up. Take some thread (see separate post on thread sizes) with you when you are purchasing your needles so you can be sure of the sizing.
Leather harness called Egg Eye needles (#4) work very well with most thread and are available in leather shops.