Get it checked
Have your CV and covering letter proofread by a native English speaker. This is important because people really do judge your ability by how you express yourself. Quant Finance is an international sport, with speakers of every language, and the ability to communicate difficult ideas is important, and if you can't get the name of your university correct, it makes one wonder if you can explain your views on jump diffusion. Also CVs use a particular style of English, which is subtly different from the one you learned in school. As there are a lot more applicants than jobs, the early stages are optimized to filter out those who stand no chance of getting in. Thus you must take considerable care to make sure you don't fail at an early stage because of trivial errors.
In your covering email, mention where you saw the advertisement and, importantly, which job you are applying for. If you don't say which job you are applying for, you are relying upon the person receiving your application to guess correctly. That does not always happen, and the larger the firm, the lower the probability, and at the very least it makes their lives harder, which is not the way to start the relationship.
A good format for a covering letter is to respond to the job specification point by point. State your ability to handle each item, together with why you think you can do it. This makes your CV more digestible, and shows that you are serious about the application.
Opinion is divided about whether you should have some 'statement of intent.' If you can think of something useful to say here, by all means put it, but be aware that a lot of new entrants to the market 'want to pursue a career in finance with a leading firm.'
Above we emphasize getting your CV checked, and this applies especially to the covering letter. Some managers discard the CV unread if the letter is sloppy.
Fonts and layout
Some things oN YOUR CV are important, and you may want tO draw their attention to them. Do not do this excessively, it is really irritating. The only time breaking THIS rule has worked to our knowledge Was a hardcore programmer who learned the POstSCript language that PCs use to talk directly to printers and he developed A program that printed his CV 3S concentric spirals of text in varying size. Viewed on Screen it would slowly spin. YES, Dominic hired him. if you're not prepared to spend at least a month learning reverse Polish notation, use a standard template. (Stick to two main font families, a sanserif, such as Arial, for large headings, and a serif font, such as Times, for main body text.)
Make a PDF if possible. These have a more professional feel than Word documents, they do not have virus problems (yet) and they retain original fonts and layout. Whatever software you use, print it out to make sure that what you see is really what you get. Perhaps view on, and print from, another PC to double check.
Give your document a name that will be meaningful to the recruiter. Call it YourNameHere.pdf and not CV.pdf in the spirit of making it easier for the recruiter. It's not nice to have a large number of files with the same name, and it's actually quite easy to get your CV written over by the CV by someone else who also called it CV.
Make sure your dates 'join up' as much as possible. Some people in the recruitment process worry about gaps.
If you claim skills in some area, it's a good bet that you will be asked questions about it. The CV should be a fair and positive statement of what you have to offer. No one expects you to share your history of skin diseases, but you'll be expected to back the talk with action.