What is the proper way to throw objects at my assailants?

I would have to say it depends which headset you're using.

I'm playing on the Vive. The throw controls are on the secondary trigger, used by your middle finger. Objects are picked up by squeezing and holding said trigger, then thrown by releasing the trigger at the end of the throw motion. This has felt pretty reasonable for me.

My buddy is using the Samsung headset, and those controllers only have one set of triggers. I'm not sure how the throwing controls are implemented there.

Edit: On re-reading your question, I don't know what you refer to as the 'move' button. Could you elaborate, and mention which headset you're using?

Edit 2: Given that you said the controls are similar, the only information I could add is to make sure you release the throw button before your arm stops moving. It hasn't been foolproof for me, but works a majority of the time.

Try not using a throwing motion but instead a pushing motion with the said object in the correct orientation in your hand.

If you've ever played darts, using that throwing motion helps with accuracy because it lowers the chance of jerk motions ruining the arc. If not, look at this example. Move only your forearm, not the whole arm, and try to keep your wrist still.

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Just as a general, both me and my guests have struggled with throwing objects in many but not all VR games.

It's not as easy as it first appears, and most games tend to only model the arc based on the (last) movement of the hand instead of accounting for the inertia of the object ever since you started moving it.

This is no different from back when clickdragging (with inertia) became popular, and early instances would often suffer if your very last move before releasing the button was a slightly different jerk motion.