How does Lennie get George into problems?

Well, If you read the book, you should know that:

Lennie commits some murders ranging from killing mice, to killing puppies, to killing women. (His inability to recognize his own strength.)

- This is not a very good thing for Lennie to be killing random things, especially human beings, while working at the barn where George is saving Lennie's ass from being fired and covering for Lennie's stupid mistakes.

As you can already see, Lennie is causing a lot of problems of George.

Other minor things that Lennie does is:

1. Not following George's commands or carrying out the duties he says he will to George.

Example: Lennie tells George that he won't kill things anymore after he kills his mouse. (He also killed the mouse that his Aunt Clara gave him). THEN he goes ahead and kills a puppy given to him by another work member/friend of George and Lennie. He THEN also kills the wife of Candy(a burly, aggressive man)... Can you see where I'm going with this? LOL

2. Forgetting to keep the promise of keeping his and George's "fatta the lan" goal to themselves and 1 other member of the farm, and instead BLOWS the secret to almost all the workers, including Candy's wife.

Hope this helps and gives you the urge to find out more of what happens in this novel.