This question might have been asked before but what side of the board should be planed first? For example, if I have a rough board or even a 1×4 and I want to make one side straight, flat and square to use as a reference for all other surfaces; would this be easiest to do with the edge or face of the board.
A board has two faces and you need to choose which one to do first. Sometimes, there’s no choice and you just need one or the other, but usually you have a choice. Many will put the cupped side down because it will usually rock less. The same goes for an arch along the length. But these mean you must plane a hump out of the material and planes often just ride along humps without removing them. Another option is to put the board cupped side up or arched side up because that surface can be easier to get flat and you can put shims or handfuls of shavings under the board to keep it from rocking. Both can be done and both are reasonable choices depending upon the board and ones needs.
If you are planing an arched (up) surface, remember that you can take shorter “scoops” out of the middle of the hump (regardless of which way the hump runs) to get rid of the hump first. This sometimes is a repetitive process in which you scoop out the middle until the plane stops cutting, then lengthen the stroke so that it cuts again and you scoop out a longer section, until, finally, you are able to run along the board to produce a flat surface. Twist can do the same thing (plane just rides over it) depending upon the length of the plane and board. It is handled similarly.
It is so, so, so much harder to develop and mate a wide face to an edge that one always does the wide first first. I might take a few swipes at the edge to see the grain or color, though.