pull your socks up
Meaning: You can say "pull your socks up" to someone if you think they should improve the way they are behaving or the way they are doing something.
- He'll lose his job unless he pulls his socks up and starts doing a lot better.
- The coach said I have to pull my socks up or I'll lose my spot on the team.
You should only say this to someone such as your child, your student, your employee, or possibly to a friend. You shouldn't say it to someone like your boss, your teacher, your parents, or anyone you should speak to respectfully.
His teacher told Jason to pull his socks up because
- they didn't look good
- he was studying too much
- his grades weren't good enough