If you're serious about landing a new job, then you need a LinkedIn profile and résumé that looks just as serious and professional as you are. Remember: First impressions count, and your LinkedIn profile or résumé may be the only impression you get a chance to make. Don't blow it!

Here are some things that will make your LinkedIn profile or résumé look really unprofessional. Avoid them at all costs.

1. The unprofessional email account

If you're still using an old, personal address that makes you look unprofessional--like cutiepie619@yahoo.com--dump it quick and get one that makes you look like the seasoned pro that you are.

2. High school jobs

Really? Mowing lawns during summer vacations and babysitting are not confidence builders for your prospective employers.

3. Misspelled words

Misspelled words, poor grammar, and typos will make you look totally unprofessional. Proofread your LinkedIn profile and résumé several times, and also have others proof it for you.

4. Personal information

Don't include things like date of birth, ethnicity, religious affiliations, reasons for leaving your previous job, or other unnecessary information.

5. Hobbies

Seriously, no one really cares that you like to knit in your spare time, or collect vintage beer bottles.

6. Your home phone number

Instead of using a home phone number on your résumé, always use a cell number. Prospective employers want to know that they can get hold of you anytime, anyplace--not just when you're hanging out at home.

7. References

This is considered filler for a résumé, and you should not include them. If a prospective employer wants references, they will ask you for them. However, on LinkedIn, try to collect as many recommendations as you can.

8. A second page

Provide the most-important information about you and your experience in just one page. On LinkedIn, try not to go on and on and on and on.

9. A photo

Résumés should not include a photo. Your LinkedIn profile, however, should have a photo. Profiles with photos get more clicks, and more clicks get you seen more. But make sure it's a professional-looking shot.

10. Gaps in work experience

Gaps in work experience make you look unprofessional. Fill these gaps with volunteer experience, an internship, or some other gainful effort.

11. Salary figures--past and future

Let your prospective employer ask you these questions in person--don't potentially turn them off before you get to make your pitch.

12. Your age or graduation dates

Leave off your age and graduation dates for high school and college. Age discrimination does exist--at both ends of the spectrum. Head it off at the pass.

13. Generic job titles

Generic job titles make you look unprofessional and boring. Reword generic, company-issued job titles so that your future employer has a better idea of what it was you actually did.

14. Long lists of duties and responsibilities

You want your prospective employer to see how you will add value to their organization, so refrain from long lists of duties and responsibilities. Instead, highlight your actual work accomplishments and how you brought value to your organization and customers.

15. The word "Résumé"