This is a key part of your job application, so it needs to be well written and relevant!
Do you need to include a cover letter with your CV or Resume in a job application? Yes! Does it need to be changed for every job application you make? Yes!
Your CV or Resume gives an overview of your skills and experience but your cover letter provides an additional opportunity to "sell" yourself by telling the company why you're applying and why they should shortlist you. Here's some cover letter tips.
Ensure all the company and contact details are correct So many people use a cover letter template and either forget to add in the company name and address or use an old one with incorrect details. From a recruiter or hiring manager's perspective, this is a real no-no and you risk getting an immediate rejection if you don't get it right. Most jobs now require candidates to have good attention to detail and if you send through a job application that's lacking accurate information, it's just leading the recruiter or hiring manager to believe that you don't have that skill.
Address the cover letter to a person where possible If the job advert has a name to send applications to, then make sure you address your letter to that person. "to whom it may concern" or "dear sir or madam" should only be used if you can't find out who to address it to personally.
Read the job advert carefully Highlight the key skills and experience in the job advert that match with yours and then think about how you can demonstrate you have them. Keep in mind that you don't need to mention all of them - just the ones that are key to the role and don't forget that any statement in a cover letter or CV / Resume, always needs to be supported either through examples at interview or via a referee.
Think about the words you're using Keep your sentences clear and concise and be genuine in what you say. I've seen far too many cover letters where the reasons given for an application or why the company is of interest is like reading from a "how to write a cover letter" manual! You need to make your application sound personal to that job and company and not just the same words that you use for every application. By all means feel free to add some of your personality into your cover letter as you want to capture the reader's interest, but just be honest and genuine with your words.
Keep the information relevant! Don't fill your cover letter with heaps of irrelevant information. You ideally want to include (a) why you're applying (b) what specific experience you have that matches what the company's looking for and (c) what key skills you have that you'd bring to the role. You can add other details as well, but make sure everything you say is specifically related to the role. There's no point adding in that you're an expert at Excel if it's not specified as a requirement.
Work Visa information/Migrating to New Zealand If you're on a work visa, it's a good idea to add some information around what type of visa you hold, the expiry date and what would be required to change your visa (if applicable). You don't need to go into a lot of detail - just enough to reassure them that obtaining a visa variation isn't going to be an issue. If you're looking to relocate to New Zealand, it's a good idea to add in some specific information about where you are in the process, whether you're working with an immigration consultant and what type of visa you'd be looking to obtain. Companies here are very open to considering overseas applicants when they're able to look offshore, but just stating "I/my family want to relocate to New Zealand" doesn't sound as if you're genuinely committed and know what's involved.
Redundancy information It's always a good idea to address this in your cover letter - perhaps by including it in why you're applying for the job. It's certainly not going to be seen as negative by the company and in some instances, could be seen as advantageous if you're available to start a role sooner than someone who has to give a month's notice.
Finally, try and keep your cover letter to a single page and check, then double check your spelling and grammar before you hit the send button!