If a firm asks for your CV, they'll expect a cover letter too. What should (and shouldn't) a cover letter, well, cover?
Address your letter to the head of Graduate Recruitment / training principal by name (the firm's website or LinkedIn can help with this).
Start by explaining what you're applying for, when you'd like to start and where you saw the vacancy advertised. (For example, "I'm writing to apply for a training contract with your firm commencing September 2016, as advertised on your website.")
Be specific about why you're applying to that firm. "Dynamic work environment" could be any company in the world - do your research about what makes this firm stand out.
Make sure that your cover letter is well under one page in length - no recruiter will wade through two or more pages and still want to read your CV.
Leave out your career highlights - mention one or two of your strongest achievements and how they've developed your skills.
Ignore the instructions - sometimes firms will ask you to address particular points in your cover letter, or hand-write it, or address it to a particular person. Double-check the application details before you submit.
Omit details about why you are suitable to the job. Be specific - what is the firm looking for, and how have you demonstrated it?
Use generalised statements or clichés - be clear and succinct about why you're applying for the role.
Sign off with a nickname - it's a formal letter. Use "Yours sincerely" and write your name and surname in full. (You'll use "Yours faithfully" when your letter isn't addressed to a named person.)
See how we can help with your cover letters.