Start with side planks before attempting front planks
We want our spine, hip, and knees all in one line.
Should feel this on your down side of abdomen and on the outside of your downside hip
If it hurts your shoulder other modifications have to be made and a different exercise selection needs to be chosen.
Start with side planks from the knees for 3 sets of 10 second holds
Once you can maintain a neutral spine (good posture during exercise) for greater than 5 sets of 30 second hold without shaking or compensations you can progress to side planks from the feet starting at 10 second holds and building up from there