On knees and elbows you will notice that the fan or wing has a tendency to warp upward as you raise. You will need to bend it down periodically to keep it out of your way as you form. The side of the piece with that fan will need to be pushed down as well with a few firm whacks once in a while. In these areas you can strike further away from the contact point to tame it into shape.
Here is the knee with the warping tamed down a bit but it still needs some more work.
Now the raising portion is finished and the knee is looking like a knee.
It is hard to tell from this photo but the curves on either side are uneven. Notice in the photo that the right side is not as curved as the left. This can be easily fixed with some softer hits to the inside of the piece over an anvil.
I use the larger hammer on the areas with less curvature and the smaller hammer in areas closer to the centre of the knee where the curves are tighter.
These hits shouldn't be too forceful but should strike the point where the piece contacts the anvil. Go over the areas that need to be brought outward or need a little more curve on the sides.
Now the knee cop area is all evenly formed and ready for planishing.