What do I use for constraints?

I'm currently developing an inverse kinematics system and got t$$anonymous$$s far https://youtu.be/SXB5rRf31Og . Unfortunately as seen it the video the bones go all over the place and it doesn't look natural. What could I use to fix t$$anonymous$$s, I was t$$anonymous$$nking of adding constraints but have no idea where to start (w$$anonymous$$ch joint to add and use). I would appreciate any feedback and what I could do to improve. THanks!