With just four weeks to the written exams you should by now be well settled into a routine that includes getting proper sleep, good eating habits, effective study practices and sufficient down time to get exercise, fresh air and socialise sensibly to avoid getting tired or stressed.
You should by and large have finished your courses of study and the last few weeks should consist mainly of revision and practising past papers. You should be very familiar with the layout of each paper.
Do not wait until the last minute to get what you need for the exams. Get your equipment in order now; calculators, set squares, compass, pens and pencils etc. Have some some convenient bag or container to carry them in. Consider writing out a check list for everything that should be in it, and keep it in the container so that you you can double check that nothing is missing a few days before the exams.
If there are topics that you have difficulty with get help now, from fellow students who know the topic and can explain it, from your teachers in school, or some other expert in the subject. If you need help, ask for it. With non-exam students easing up as the summer approaches, Galway Maths Grinds have some free time slots for one to one sessions.
Keep a copy of the timetable in a convenient place and plan how you will get to the examination centre each day. Allow time for any potential hold-ups in traffic etc. The secrete to avoiding panic and staying calm and composed is to be organised.
Its probably a good idea to cut out things like late night television, and ease up on distractions like facebook, if not cut it out altogether. As far as practical avoid people who are negative or stressed about the exams as their negative attitude may work to undermine your own confidence.