First planing a face to get a flat surface. I use a foreplane with a cambered blade. I set it rather rank, but not too much. The wood is quit hard, so you want a setting that doesn't wear you out too much. Now it is a matter of removing the rough sawmill cuts and at the same time to remove all bow, cup and twist in the board. First planing across the grain, then diagonally and finally along the grain.
All the time while planing with the foreplane and the jointer I check the surface with a straightedge and winding sticks. I do this often, because it is very easy to introduce a convex surface. Here you can see the two winding sticks on top of the board, they are pretty parallel allready.
When the first face is flat, I start to straighten the side of the board, perpendicular to the flat face. Put it in the vise and check the grain direction. It's always best to try as much as possible to plane with the grain. Wallnut isn't a difficult wood to plane, but you don't want to make it more difficult then neccessary. In this picture the best planing direction is left to right.
Straightening the edge and making it perpendicular to the face is a bit of a juggling act. I check the perpendicularity with a small square. Correcting it by offsetting the plane to the right or the left, or even following a diagonal course. I use the fingers of my left hand as a fence to direct the plane.
Overall I don't shoot for perfection. It is good enough when it looks right and when the area for the joinery is nicely flat and square. The face and edge that have been planed now will be the reference faces for all further work, so I mark them accordingly.
Next installment is thicknessing the board and straigthening the other edge.