I can crack my elbows by using one hand to stabilize the arm then add resistance against the hand that stabilizing the arm. It is more of a pop then a crack. I've devolved this after breaking my arm and once it was healed the doctor who set the arm (aligned the bones back up) performed that crack on me and ever since then I "stole" it and now can do both elbows very well, although my left arm (the one I broke) pops a lot better than my right.
BTW, if your reading this and want to try my method of cracking the elbows, make sure you move your elbow up and down because some spots it will crack and some spots it won't. You need to find the sweet spot. My right arm cracks at about a 45 degree angle in the elbow. My left cracks at a lesser degree than my right. Why? I have no idea. I'm I'm being obsessive about cracking them I start with my arm against my body then move farther and father away from the body just to make sure there are no more pops left.
Starting out then going in is bad because it's more unnatural. I've popped it going in and it hurt very bad.