Remember, when people gather together and pray no prayer gathering is a failure. When you're authentic, aware of personal styles and atmosphere you'll see students connect with God and each other. As you prepare an environment that enhances prayer you'll help new and younger Christians learn how to pray in your group. Help them feel relaxed. They don't have to say anything if they don't want to.
People tend to pray after they've watched others pray.
Reassure students that silence is not a problem and they don't have to fill empty space with words if the group is quiet. When students speak, encourage them to be brief so that everyone has a chance to pray. Since people usually have personal prayer requests to share you need to consider how to handle those requests. Often a group spends 20 to 30 minutes talking about requests then squeezes in five minutes of actual prayer before ending. Sometimes that's not a problem, but if your time is limited there's other ways to handle requests.