Ten Things to Check
1.  FOLLOW DIRECTIONS CAREFULLY
         
This is the most commonly made error by applicants; be sure that you follow the directions thoroughly.
2.  WRITE LEGIBLY
         
If you do not apply online, the first impression is your penmanship(handwriting).  Your application should be neat and readable.
3.  PROOFREAD EVERYTHING
         
Be sure to proofread everything you write. 
4. CHECK SPELLING AND GRAMMAR
          
Poor grammar and spelling will  give a bad impression.
5. ENSURE EVERYTHING IS FILLED OUT
         
Make sure you fill out all sections of the application that pretain to you.  If possible do not leave any blanks.  If the question does not apply to you, reply "not applicable"(n/a).
6. FILL IT OUT YOURSELF
          
You can get your friends or parents to help you to brainstorm if needed, but fill the application out yourself. 
7. LIST EXTRACURRICULAR ACTIVITIES
           
List only the extracurricular activities you have participated in.  Some colleges do check. All extracurricular activities do not have to school related.
8.  CHECK THE DATE AND SIGNATURE
          
Don't forget to sign and date the application.
9.  ATTACH ALL PERTINENT INFORMATION
           Make sure you attach all supporting documents the application requires.  Be sure to check with admissions before sending these documents electronically; you may have to send them by snail mail.
10.  ENSURE YOUR  ONLINE APPLICATION GETS SUBMITTED.
           
If you are applying online, be sure that you reach the confirmation page.  Always save correspondence from your chosen institution and confirmation e-mails.  Keep copies of documents submitted online or through the postal services for your records. You never know when you may have to refer back to those papers.

"10 Things to Check Before Submitting Your College App" by Ross Blankenship, The NextStep Magazine