THE ONLY WAY TO GET BETTER IS TO DO AS MANY PROBLEMS AS YOU CAN.
Here are a few resources:
For those who would like to strengthen their problem solving/ basic competition math skills, we highly recommend Art of Problem Solving's Alcumus.
Alcumus Link: http://www.artofproblemsolving.com/liz/Alcumus/index.php

Do as many past math competition Problems as you can.
Here are a few competitions you can find problems for:
Mathcounts School Round Problems
Mathcounts Chapter Round Problems
Mathcounts State Round Problems
Mathcounts Nationals Problems
Mathcounts Handbook Problems
AMC Problems (AMC 8/ 10) - Do every year.
Utah State Math Competition Problems
Utah Math Olympiad Problems
Math Kangaroo Problems
Snow College Math Competition Problems
and many, many more.

ON MISSION MATH UTAH'S WEBSITE, THEY HAVE MANY FREE PROBLEMS AND THEY WILL BE UPLOADING MORE. 
missionmathutah.com

Here are other links:
http://www.artofproblemsolving.com/Forum/resources.php?c=182
http://www.utmath.org/https://www.artofproblemsolving.com/Wiki/index.php/AoPSWiki:Competition_ratings
http://amc-reg.maa.org/reports/generalreports.aspx