Where it picks-up the most signal, both quantity and quality...
You'll need to do some expermenting to arrive at that best spot. If your property has no obstructions, that could be almost anywhere, but the closer to your set the better. Otherwise make sure it's a clear "look" from the input end of your antenna in the direction of the towers you're trying to receive. There are many ways to mount it. Pick one that makes sense to you. Higher is better for signals, but worse for just about every other consideration, e.g., wind loading, lightning, cable length, etc. Definitely stay FAR away from power lines of any sort, mostly for safety but also due to interference, and make sure the system is properly grounded. If you're unsure about any of this - better have a professional handle it. Good luck!