Great question!! Many people have a hard time with this part of management, so don't feel like you are alone on this one. I am going to speak from my experience as a former Marine Corps officer and as a private sector project manager. I have used this process successfully, both as a military officer and as a civilian project manager. The best way to hold people accountable is to let them know right from the start what they are being held accountable for. If they don't know what they are being held accountable for, it makes it really tough to try to hold their feet to the fire. So how do we do this???
I like to establish date goals. Let the leads know what the key dates are that they need to achieve. Let the leads know any other expectations that you have. Be clear. Be concise. Get their input into the upcoming project. Give them the opportunity to review the plan if they didn't have input already. Tell them that your job is to remove obstacles. And if they have obstacles, they need to bring them up to you. This doesn't mean that you are going to do their work for them. But you will do your best to remove obstacles. Legitimate obstacles... From their, do your weekly stand-up meetings and get their status reports. If someone is not hitting the mark, pull them aside separately and reinforce the point... "You are responsible for hitting this date. Why are you falling behind. Do I need to step in." These conversations don't have to be accusatory. You gave them a deadline. Emphasize that the deadline has to be met. Use your judgement and determine what the root cause is. They want to succeed, but sometimes they need to be pushed. As long as you are clear on expectations, you shouldn't have any problem. Give them ownership. And then hold them accountable...