i regularly receive CVs.
I hate cover letters that are too short. I have literally had "I am applying for this job, CV enclosed". This was from an internal candidate who reckoned I knew him already. I had to quietly point out that more than one person was on the interview panel, so a bit of effort wouldn't go amiss.
Conversely too long is awful- do not waffle on about your lifelong commitment to the role, we take it as a given you want to do it, and love the career, if you are applying.
Write your cover letter mentioning a few qualities or skills, then write your CV wth the job advert in mind.
Eg you might say you are an expert in your field; however, if the job advert asks for a particular niche make sure you big it up if you have it.
Keep your most recent experience at the top of your CV.
Don't miss out vital info worrying about being PC. I am not too keen on CVs without a DOB on them. Usually you can roughly work out a persn's age by their experience, so why hide it and why make me half to guess? As an employer real life experience is important to me, so if I see an application from someone in their 40s I would be thinkng, brilliant, they will bring loads to the role, so I would be more inclined to call them for interview.