If you aren't satified with someone and want them to do better, you can tell them to pull up their socks. (www.usingenglish.com)
He's going to have to pull his socks up if he wants to stay in the team. (thefreedictionary)
You can take breaks or naps, but the clock continues to tick as you do so; generally, it behooves one to just pull up one's socks and keep going.(Google)