So here are my five cent:
The question why you want to be hired by especially that company is important to answer: of course you may apply by different companies that appear fairly similar - e.g. two different publishing houses tat both publish travel guides. In any case you should have an answer in front of company A why you chose it. (And a different one for company B).
And : if you sent printed materials (and not e-mails): make sure it is good clean white paper ( a little heavier maybe than your average printer paper), there are no typos, there is not too much design (unless you are in advertising or something artsy) and you sign it properly. It is what first gets the attention.