Lie and Lay -- Two of the most often misused verbs
We will right away get rid of the verb lie when it means to tell an untruth. Everyone knows how to use that one! Let's look at the ones that give us so much trouble.

Lie - to recline
lie - present tense
Examples: I lie down every afternoon for a quick nap.
My baby lies on the sofa for his morning nap.
lay - past tense
Examples: Yesterday I lay in the hammock and enjoyed reading my new book
The children lay on the floor and pretended to be asleep.

lain - past participle (used with helping verbs)
Examples: Have you lain on the new mattress?
To protect her skin, she has never lain in the sun.

lying - present participle (used with helping verb)
Examples: Were you lying down?
They are lying by the pool.
The book is lying on the table.

Lay - to place; to put

lay - present tense
Examples: I lay my keys in the same lace every day.
He always lays his books on the stairs.

laid - past tense
Examples: She laid the pillows on the bed.
I laid the comb on the dresser, and now it's gone.

laid - past participle (use with helping verbs)
Examples: Mom has always laid her purse on the hall table.
I wish I had laid my keys in a safer place.

laying - present participle (use with helping verbs)
Examples: Sue has been laying the rocks around the flower bed.
John and Buddy were laying bricks for the new wall.

Have you noticed anything about the examples? Of course!!! The verb lie never has an object; the verb lay always does!
Then why do we have so much trouble with using the right verb? Perhaps it is simply that the form lay appears in both. Here are some "always" rules to remember:
Never use laid when referring to reclining. It always means "placed."
Never say "I laid down" or "Please lay down."
Instead say "I lay down" or "Please lie down."