Two verbs that I struggle with are lay and lie.
Lay means to place or put. The past tense is laid. We speak of laying something on something, such as laying a book on a table, or if you did it yesterday, you laid a book on the table.
Lie means to recline. Many times it is used with the adverb down, as in "I would like to lie down on the bed." Here is where it gets really fun: the past tense is lay, just like the present tense of the other verb! The past participle is lain. If I decided to lie down, I would lay on the bed for a while, then realize that I had lain there too long.
I don't know about you, but I'm exhausted just thinking about it. I need to go lie down!