The blitz approach to job search is unfortunately alive and kicking but it yields poor results and leaves job hunters frustrated and more demotivated. Sending your CV to 100 employers by post or email isn't a strategy I recommend. Lots of people play the numbers game, it seems logical. If I send 100 CVs at least one of them will yield a job wont it?
But it rarely does. Unsolicited mail ends up as spam or goes unread because unless an employer has a current opening, they don't waste time scanning CVs. In fact reading CVs is consistently rated as one of their least favourite things to do so they avoid it where possible.
When they do have an opening, they will give your CV about 25 seconds of their time before they decide if they will bin it or read on.
A CV needs to be personalised and tailored for each job you go for if you want it to be read. I'm not suggesting you have 25 versions of your CV. The core achievements and key qualities should always stay the same. But you will need to emphasise different activities or leave some stuff out it's not relevant, depending on what you are going for. And you won't know what an employer is looking for unless you are in receipt of a full job description and ideally have had a conversation with them.
Calling an employer prior to sending a CV gives you a chance to check what they are really looking for and get a bit of rapport going. If you are prepared to call several times to catch them and (avoid leaving voicemail messages which don't get returned) ask the right questions, you will gain information that will give you competitive advantage over other applicants.
This then helps you to craft a more personal CV and cover letter which matches what you have to offer with what the organisation requires. You can really set yourself apart from the competition if you hone your cover letter writing skills to only focus on the employer's needs (based on what you learned from talking to them) and then spell out why you can do it.
Follow up on each and every CV and cover letter you send. I think 4/5 days after you submit is a good rule of thumb and you will yield better results and find you get more interviews this way.