It is amazing how students who have spent almost six years in second-level education, and who excel at some of the toughest examinations in Europe, can make so many careless errors when filling out their CAO forms.

Last year large numbers of students made mistakes. Some put down codes for courses which did not exist, others put degree courses in the certificate/ diploma list, while others left out elementary information like when they were born.

So let's go back to first principles. The form is a fairly innocuous piece of work, but like most forms, if you assume it is simple you will make mistakes. Compared to other forms you fill out in your life, this is an important one and getting it right saves you having to do it again during the precious period leading up to your exams. If you make a mistake on your form, you will be asked to fill it out again by the CAO and you will have to pay £5.50 for the pleasure.

Show the form to your career guidance teacher when it is completed - it is of course advisable to have discussed the whole process with your career guidance teacher first. You should also have read the college prospectuses and carried out other research. The form itself is four pages long, but most students will only have to deal with the first two pages (the last two are for special category students). The first few sections are simple. Just write down your name, address and put the correct date of birth in a special box. There is no need to enclose a birth certificate, but be careful - some geniuses last year put the date on which they filled in the form into the box rather than their date of birth.

In the box for your address, do not put down your school address. Put down the address where you are most likely to receive correspondence, obviously in most cases your home. After filling out the basic sections, you come to the most important part - the list for degrees and certificate/diplomas.

It is important because if you put down an incorrect code, the CAO will not know it is incorrect. Their machinery will simply read the code and presume it is the course you want. So make sure if you put down a CAO code you know which course it corresponds to.

You are allowed to put down 10 courses on the degree list and 10 on the certificate/diploma list. For those interested in nursing, there are another three lists (general nursing, psychiatric nursing and mental handicap nursing), each with 10 options.

But for the vast majority of candidates the non-nursing lists are the relevant ones. Make sure you put down courses that you are eligible for. For example if a course requires a certain language or science subject and you don't have it, do not waste time on it (see the charts in this supplement).

Another mistake is putting degree courses on the cert./diploma list and vice-versa. Also make sure you tick the box at the end of the form which asks whether you are a special category student. Included in this section are mature students, those who have taken British exams like GCSEs and those who have already received an education from an Irish university or institute of technology. They have to append additional information to their forms.

You must supply the CAO with a photocopy of pages three and four of the CAO form for each higher-level institution to which you are applying. Equally, any other attachments with pages three and four must be photocopied so there is a set for the CAO and each college.

When you have figured all this out you can turn to the lists themselves.

Many students leave the cert./diploma list blank because they are only interested in degrees. Ironically, if you do this, you could be cutting yourself off from degree options down the line.

Remember there is a path from cert. to diploma to degree and the number of add-on degrees available is increasing each year. The CAO allows you to list up to 20 courses in all, and you should try and use this facility to the full. The vital thing is to list the courses in order of preference, starting with the course you most want, not the course you think you will get the points for.

Every year, the Irish Times help-line receives tearful phone calls from students who did better in the Leaving Cert. than they expected. This is because they based their choices on a wild guess about how many points would be enough - an inexact science. Also, do not underestimate your potential Leaving Certificate performance and leave out certain courses you like, but think are too high-powered for you. The opposite is true as well; don't put down courses solely on the basis that they are high-point courses.

If you are offered your first choice, you will not be made any further offer. All of the courses listed below the course that you were offered are effectively wiped out by the CAO computer. You can move up the list but not down.

Bear this in mind as you fill out your form. Before you post off your form, you should take a photocopy and keep it for reference. Don't forget to get the certificate of posting, on the back page of your CAO handbook, stamped.