I found this on a new-to-me site called freesurftips. When you get your first SUP board, you may wonder how to carry that beast down to the water. Well, here’s one way to do it (and I’ll be featuring more in coming days):
How to hold a stand up paddle board Although many surfers and non-surfers paddle their SUP for exercise and conditioning, carrying a stand up paddle board improperly could result in unnecessary stress on the neck and back. Here is an explanation of how to carry a stand up paddle board the correct way. 
First, make sure you have plenty of room so that you won’t ding your oversized paddle board. Lay your paddle out or prop it up somewhere so that you can pick it up later. Place your dominant hand on the closest rail of the board, and your other hand on the far rail. Bend at the knees and lift the board up and over your shoulder.
Now, lower the board onto your shoulder, supporting the load with your upper-back, shoulder, and arm. Continue to grip the rail of the board with your dominant hand. You can now release your other hand and drop to a knee while you pick up your paddle, holding it about 2 feet from the blade. Keep your back straight as you stand up using your knees. Now you’re ready for the long walk to the water!
If there is wind, you can grip your paddle and stabalize the board at the same time, using your dominant hand. To put the board down, just reverse the steps and lower it off your shoulder. Bend at the knees and carefully lay it down. If the sun is out, lay the board upside down, with the fins up, to protect it from the sun.