Applying for jobs can be a complicated business, with different businesses demanding different things from their job applicants. Understanding how to individually target these businesses to improve the results is ideal, but isn’t always realistic. In sintances where very little information about the business is available, basing your contact with them around providing them with mostly relevant information, with a short cover letter, acting as introduction to you, with both a bit of information about your experience and professional history, as well as some about your motivations, why you’re applying for the job, how you believe you will be an asset to them. This shouldn’t be very long, so writing between 150 words and 500 words is your best option. If the job you’re applying for has a lot of competition, limiting the size to the smaller side of things will be best, as the person reading it will have to read hundreds of them, and the impact of it will be reduced after a while.