Don't slack off. Make sure that you turn in all of your work on time, and make sure that you check for any work that you might have due regularly. Don't screw up and spend the whole night just playing videogames. It only gets harder from this point onwards. Hold your head up high and do your best. The world is yours for the taking, but only YOU can forge the path to take it. There is nothing that you can't do. Listen to your mother and tell her you love her everyday. She will not be there when you go off to college. Do not be afraid to lean on your friends for support and in turn be the the light in their times of darkness. Hold your head up high and smile. Let the world know that no matter what happens that you'll face it all with a grin. Never falter or look down, BUT look back upon your past failures and learn from them! You can do it! Everyone believes in you! Make them proud!
The same thing I tell current high school students which consists of telling them to stay in school. There are student loans and scholarships for us to continue our education.