When I was first learning to ride frontside in side-on conditions it quickly occurred to me that I was simultaneously forced to improve my upwind riding ability in order to regain the ground lost when riding frontside. The two things go together when riding in our conditions here on the Great Lakes.
This article will focus mostly on how to go upwind on wave gear, although I will make a few mentions and brief comparisons to freeride gear.
Let's start with the objective. Getting upwind. If you want to get upwind, start by looking upwind. Turn you head and look upwind. When you do this it will turn your front shoulder out a bit. This begins to put you in the proper stance. Now, let your body shift slightly toward the nose of the board. Allow your front leg to bend as you put weight on that front leg, while straightening the back leg. At this point it's obvious that you have shifted your net weight forward on the board. Even your hips have shifted slightly forward. You can also remove your rear foot from the footstrap and place that foot directly in front of the rear footstrap. Some riders find this very helpful to get upwind, although I generally prefer to keep my back foot in the strap for overall control. Remember that speed is your friend while doing all of this. The more speed you have, the more lift you get from the sail and the fin.
So you have a good stance, but that alone is not enough on a wave board. Your fins are small, so you need the rail of the board to help you get upwind. Weight the heels of both feet, but especially the heel of the front foot. This will put the entire board on its side. The rail will then help propel you upwind like a kiteboard does. Remember that speed is your friend while doing all of this. The more speed you have, the more lift you get from the sail and the fin.
But this is not the whole story. Burn the following mantra in your brain. When your harness lines are back it helps you sheet in. Move the front hand closer to the harness line and it further helps to sheet in and power the front of the sail. All of this puts pressure on the mast foot. The pressure on the mast foot keeps the nose of the board down. And by keeping the nose of the board down you prevent air from getting under the board which reduces the spinout problem. Repeat this mantra over and over in your mind.