Do you often raise your arm? Maybe you drink a lot of tea, or when you talk, you wiggle your arms around gesturing. If it sounds like you, you might want to turn off Wake Screen on Wrist Raise, a feature that shows you time and alerts when it detects motion.
Open the Watch app on the iPhone. From the My Time tab, click General> Off Screen, and then click the slider at the top. It is a drastic decision: You will find that some activity measurements will not be available and your clock cannot lock or unlock automatically. So play for a bit and make sure this is the best option for you.
Now, to activate the clock, press it.