My advice specifically concerns resumes, and how to get your resume noticed. I don't know how important that would be for you (it sounds like you're after entry-level positions), but for me it was extremely important to get my foot in the door for a professional programming position.
First of all, when you send a resume, it usually has to get past a couple stages before you get a phone call back:
1) These days, when you first send a resume off, usually a computer scans your resume for key words instead of a human looking at it.
2) If your resume has the right key words, then a human in the HR department will look at the resume.
3) If you get past HR, they'll submit your resume along with a couple dozen other candidates to the hiring manager.
4) The hiring manager will choose a few resumes out of HR's pile for interviews.
5) This is where you get the phone call, if you managed to get past all of these screenings.
Thus, to even get noticed, it is VERY important your resume has the right keywords in it. I'm going to tell you how to find those keywords. It's actually pretty easy to do and even a little bit fun.
Do you know what a word cloud is? Basically, a word cloud is a collection of words bunched together in a cloud-like formation. That much is obvious, but typically the more important the word, the bigger it will be compared to the other words. There are lots of websites out there that can generate word clouds automatically for you, if you give them text to work with. Just type in "Word Could" in google and watch all the word cloud websites pop up.
http://www.wordle.net is an example.
What you want to do is take the job description from online and run it through a word cloud generator. Then when you get your word cloud, all of the important words will be exposed immediately as the largest words. Make sure that your application/resume mentions all of those important words at one point or another. Those words are what the screening software and HR will be looking for. As soon as I started using this method, I got a lot more calls back. I had one day when I had THREE interviews scheduled, and one of them led to the great job I've got now.
Naturally, the important words will be different from job description to job description, so you need to reword your application/resume for each position. Make sure you make a custom application for every position you apply for. It's also about quality, not just quantity.