As with any letter, the intention letter that is attached to your CV should be well written. It should clearly explain why you are applying for a job position with this employer. You will want to keep this first paragraph brief and to the point. You do not need to embellish the facts, simply state why you want a position with this company and what that position would be. You can even add how you found out about the position, was it from the local newspaper or you can let the company know if another current employee has referred you to apply for the position.
The next element of an intention letter should be why the company should hire you. You want to explain very briefly again; your qualifications and what you would bring to the company. This part of the intention letter is the most important part so you want to make sure it is well written as well as brief. You should be able to do this in one long or two short paragraphs in total. Any more than that is over kill and not necessary as you are attaching your CV or resume which has the same information in more detail.
The final element should be your closing statement. You want to thank the prospective employer for their time in reading your CV or resume. You may also want to say how enthusiastic you are about working for the company and that you would be an asset. The main fact to keep in mind is to be brief and to the point. The person reading it should only have to glance to get the main gist of your intention letter. Your intention letter should never surpass one page of written text. An intention letter is simply a brief introduction to your prospective employer that will introduce them to you.