Go to societies, even if it's just taster sessions during welcome/freshers week - you'll meet people who aren't on your course and if you like a society they're a great way to get a break from studies and see people once a week. Go to all your lectures, you'll be able to get to know your coursemates and lecturers better if you do and it's going to help when it comes to assignments (plus you'll just learn so much more). Start assignments early - slow and steady can be really helpful to get things done well and it means you won't have to sacrifice all your social/relaxing time during deadlines season. If something is happening that intrigues you, go along to it (whether that's a flat party, an SU event, a one-off evening lecture etc.). If something you don't want to do is happening, don't let anyone bug you into going.
I feel like this may seem like typical uni advice but, genuinely, it's what worked for me. Going to the RPG+LGBT societies during my first year got me my two closest uni friends. Then going to lectures and developing the habit of starting work early has alleviating a lot of stress and helped my grades improve.