In many ways, the hiring process is a minefield. Step in the wrong place (figuratively) and you can blow up your chances.
A lot of desirable jobs have more applicants than most companies would even consider interviewing. This means that even if you're qualified, the person doing the hiring might be looking for reasons to not hire you. That sounds harsh, but what else would someone do when faced with a pile of similarly qualified people?
As easily as you can make a mistake before even landing an interview, there are ones you can make during one, or afterward, that can also cross you off the list.
1. You fail to address what's in the ad
If the job listing says "some Spanish helpful," and you don't speak any Spanish, you need to address that in your cover letter. You can't immediately learn a skill you don't have, but you can show a willingness to work toward attaining it once you have the job. It's even worse if you do speak Spanish or possess some other asked-for trait and don't communicate that in your cover letter or on your resume.
2. You're slow to respond
Sometimes, if a job listing has a closing date, the employer waits until all the applications are in and then finds the best few to interview. In many situations, however, employers post an ad and contact qualified candidates as they come in. If you wait a few days, you might find yourself not getting interviewed for a job you'd otherwise have had a shot at.
3. You're late
The most basic test at an interview is whether you can show up on time. If you're late -- unless there is a truly significant disaster that would make anyone late -- you are showing disrespect and creating doubts about your reliability.
4. You're unprepared
You should come to an interview dressed appropriately -- in conservative business attire, unless specifically told otherwise by the interviewer. Bring copies of your resume to hand out if needed, and be ready to ask questions that show you've researched the company.
5. You boast about your accomplishments
Don't talk about how great you are without backing it up. Go into an interview prepared to discuss not just your accomplishments, but also how you achieved them.
If, for example, you raised sales by 10% by changing the commission structure to one that rewarded harder workers, explain what you did. Be prepared to answer questions challenging your accomplishments with details and data where appropriate. And be humble, but not bashful.
6. You forget to say "thank you"
As you leave an interview, thank the interviewers for their time. Once you get home, send thank-you notes (by traditional mail or email, depending on how you've been communicating).
Use a thank-you note to restate your interest in the job. You can also use it to clear up a point from the interview where you might have been vague or didn't have a good answer.
Make it a job
In many ways, finding a job is a job in itself. Approach it as such by devoting time each day to the search, sending resumes, and preparing for interviews. Do everything you can to put yourself in the best position possible, so the person doing the hiring has a harder time finding a reason not to hire you.