Most of the reports I've read or heard suggest 1-3 tablespoons of oil per day for an adult. I did a little research several years ago and found that the oil content of the seed varies in the range of about 20-35%. So, 3-4 tablespoons of seed one or two times per day should be fine for most people. Practically, this works out to something like just filling the bottom of the typical tabletop coffee grinder each time.
There is a more precise answer to your question but I don't remember the number. It has to do with the ratio of the omega-3 to omega-6 fats in your diet. The omega-6 fats are common in seeds, nuts and other foods.
If you buy flax seed oil, you'll find that it is and must be refrigerated to keep it from becoming rancid. The seed can be stored at room temperature because it has a tough shell which protects the oil from oxidation. It also protects the oil from your digestive system and that's why it should be lightly ground before being consumed. Obviously, the oil and ground seed should not be heated.
There is one other important detail that I didn't include in my above post. Besides adding the omega-3s to your diet and otherwise getting all the other required nutrients in your diet or through supplementation, it's also important to eliminate or significantly cut back on your intake of hydrogenated fats.
Hydrogenated fats are not natural and tend to reek havoc in the body, but they are common on grocery store shelves both in cooking oils and processed foods. Smith discusses the history of fats and oils in his book and there is an interesting correlation between the growth in the use of hydrogenated oils and the growth in the occurrence of diabetes and related cardiovascular disease over the last century.
For food preparation, I try to limit myself to butter, extra virgin olive oil, organic coconut oil, and flax oil.
Thank you. That was an excellent reply.