There are lots of books available from your library about study skills. You may need to find an approach to studying that suits you. One of the best study skills is to study your lecture notes the day you attend the lecture; not a few weeks later. 'Study' does not mean passively reading them in a cafe or whilst watching TV. It means actually trying to read your lecture notes in a way that you could explain the topic to someone who missed the class. If you can do that then you have really understood the topic.
Of course, if you messed up because you were partying too hard and not focusing on your studies then it's easy to party less. If you have fallen in with the wrong crowd you know you need to distance yourself from them. If you have drink or drug issues then there are counsellors at uni you can turn to for help - and keep your pastoral tutor in the loop.