How can I fix shoulder and hip pinching when rigging a cartoony character?

[Steven12]

I'm working on a short animated film in Blender and I've modeled a stylized humanoid character, but I'm completely stuck on the character rigging process. I've built a basic armature with inverse kinematics for the legs, but when I try to pose him, the mesh deforms terribly around the shoulders and hips, creating awful pinching and stretching. I've tried weight painting, but it feels like guesswork and I can't seem to get clean, smooth deformations for a simple walk cycle. Are there systematic approaches or common pitfalls in weight painting and joint placement that I should focus on for a cartoony, bendy character?