This is how I prep rough cut lumber is most of my lumber is 8 ft long. So, I have a strip of 1/4" or 3/8" plywood that is about 4 inches wide by 8 ft long. One long edge is a factory straight edge. I lay the plywood on the rough lumber covering one edge and use 1 drywall screw in each end fastening the plywood to the lumber. I then, using my table saw, run the lumber through it with the plywood against the fence. Take the plywood off. You will then have one straight edge to work from. Use your jointer to make it perfectly straight. I've had great luck doing this and have straightened many hundred feet of lumber.