First of all, are your results bad compared with your cohort, or just bad compared with the 90+% you may well have been used to receiving at school? It is not unusual for university exams to be much more harshly marked than A-levels.
Secondly, what type of exams were they? Techniques for doing well in MCQs vs SAQs vs essays vs practical exams are all very different.
Thirdly, how exactly did you revise? Did you just read the books/lecture notes? Make notes? Mind maps? Test yourself? Different people learn in different ways and unlike A-levels you can't just learn the syllabus and be safe. You need to find out what works for you and improve your techniques in that direction, with variations for the different types of exams.
Don't let a weak-ish performance in your first set of exams get you down though, work out what went wrong this time (Did you not know enough? Or were you just not able to answer the questions in the right way?) and improve on it!