The basics of woodworking is to get one face true and flat before working the other side and edges. If the board, in the rough, is not flat, I recommend making a sled longer than the board and fasten a cleat to the back end so the board will not slide off as you pass it through a planer. Here is the trick that I found. Wherever the board does not touch the sled (make sure the sled is flat on a table), add a shim underneath. You can tape it in place to hold it. These shims will keep the planer rollers from pushing the board down as it passes through the planer. This method will take a bow or a twist out of a board. Expect to lose a lot of thickness. If the board is twisted, you can put shims under opposite corners at the ends so that some thickness is taken off both ends rather than all the thickness being taken off from one end and really losing a lot of thickness in the final product.
Once you get one side true and flat, then you can flip the board and flatten the other side. Then, you are ready to true the edges. Here again, you can use a sled to rip the first edge on the table saw by having that edge hang over the one edge of the sled and using the true edge of the sled against the fence. You will need to fasten the board to the fence so it cannot wander. Once you have one edge straight and square on the table saw, then you can run it across a jointer, if you have one.
Now, you are ready to trim the second edge. Set the table saw to the width you want, or a little extra if you have a jointer, then rip the board to size.