It might help to think about chickens and eggs. Hens lay eggs (=place them in the nests). After that, the eggs are lying there. Yesterday morning when the farmer checked the coop to see if the hen had laid any eggs, he saw that two new eggs lay in the nest.
A friend used to remind himself that “only people can (tell a) lie.”
Given current studies on other primates this may not work anymore.
Primates? Hmmph.
The dog we had while I was growing up would jump off the furniture as soon as he heard someone coming.
This was as much as to say:
I think deception in the living world is much older than we realize. It probably goes back to the time some bacteria came up to the first eukarote, and said, “We just want to come in and rest a while, and then we’ll move on. Promise.” But they never left, and thus we have mitochondria today.
The simplest method of all: Use what comes naturally and sounds right to you and don’t worry about it. I have difficulty thinking of any situations in which you would need to do otherwise. To the extent that anything you say would sound out of place to most others, it will generally sound out of place to your own ears as well, without having to consciously think about it.
That having been said, you may still be curious to know explicitly what the rules are that you and ordinary speakers already implicitly follow, or the etymology and changing historical usages of those words, or what attempts (possibly mistaken) have been made over the years to formalize their rules, or various such things. But if your only concern is “How should I speak in my everyday life?”?. See above. Speak how you want.
While I tend to agree with Indistinguishable (not only in this case), relying on one’s “ear” yields results that will satisfy the prescriptivist only when one’s dominant exposure is to good writing and good speech. In those moments of self-doubt when I’ve stayed up too late reading about people “loosing there wits” on the internets, I find the mnemonic device:
“Chickens lay, people lie”
to be most helpful.
As a present-tense verb, lay means “to place” (when it does not mean "to induce to have intercourse). Lie means “to recline”. If you keep these two synonyms in mind, which verb is the preferable use in a given context will become self-evident.
Pitfalls: The past tense of lie is another meaning of lay. And a peripharstic lay construction is an older common synonym for lie: “to lay [oneself] down” – as in what the Scottish singer claims to be willing to do for Annie Laurie: “And for bonnie Annie Laurie, I’d lay me doon and die.”