Brendan Mernin, Tutor, Advisor, Writer, Parent
Great question. Before I answer it, I will say that the best way to get A's in math or any other subject is to approach your work with a level of curiosity and devotion that will lead you to a high grade. That is, find your fascination with the material and pursue that feeling with intensity. If you do, the grade will follow.
That said, here are some tips for getting high math grades:

Get enough sleep: Many academic issues can be solved by simply getting sufficient rest. If you are exhausted in school every day, you will not absorb the teacher's lesson fully. Then later, when you do your homework, you will be inefficient. Try to break the cycle of cutting your sleep hours short.

Sit in the front: A lot of students can get a boost in school by sitting closer to the teacher and the board. It's easier to understand what you can see.

Raise your hand more: Most teachers include class participation as part of the grade, so participate more and bring your average up.

Increase your neatness: Neatness in math has two benefits. First, it helps you follow your own thinking more clearly, so you can make further deductions more easily and review what you've done to spot your errors. Second, neatness makes your teacher's life easier because she won't have to work so hard to grade your paper. That translates to an edge when your grade is right on the bubble between one mark and another.

Do extra Problem sets: There's no substitute for hard work in math, and that generally comes in the form of problem sets. Most math grades can be improves by doing more math.

Ask your teacher for extra work: If you want to do more math problems, your math teacher is a good person to ask for problem sets that will target the lessons you are learning.

Imitate the A students: Never assume that the A students are doing better than you because they are smarter. They are most likely following

Do chapter reviews: Every math textbook offers chapter and section reviews that include many problems and answers for your enjoyment. Take advantage of them.

Use online resources: There are countless online math resources to help you when you're having trouble, or when you just want to learn more. Khan Academy is well known. Try Wolfram Alpha and patrickjmt also.

Try a different textbook: Ask your math teacher, or poke around the internet, for a different textbook covering the same material. Sometimes the varied presentation (and the extra practice) can make all the difference.

Redo your errors: You should redo every error you make in a math course. Doing so will automatically allow you to focus on your weaknesses and turn them into strengths.

Find a good tutor: A professional oneonone instructor can often help you understand math quickly, and show you how to succeed. Noodle.com (this very website) is a great place to find one.

Use peer tutoring: Many schools offer free peer tutoring programs. You might find a kind and patient older student who will show you how it's done. You might even make a new friend in the process.

Find some motivation: Many math students have trouble because they don't know when they will ever use the math they are learning. Ask your math or science teacher to share reallife examples of people who use the math you are learning. Or, try looking at the scientist profiles on www.math4science.org for descriptions of professionals who use math every day in their exciting work.

Study your teacher's assessments: Look through all the tests and quizzes you've been given by your teacher. How does she present material? How does she ask questions? What does she consider when deducting points?

Join the math team: If you can do so, join your school's math team. (This might be easier for middle schoolers.) Even if you are at first the worst mathematician on the roster, you will quickly learn from others in a fun and competitive environment. Many students find that they learn more quickly in a game competition context than in a classroom.

Explain it to someone else: One simple way to find whether you have learned lessons thoroughly is to try to teach them to others. A study group (see below) is a great way to find peers to serve as your "students."

Make lists of facts/rules/theorems: a proper math study sheet includes all the facts, rules, and theorems you've covered. Be sure to keep a running study guide during the year so that you can review the previous material frequently, and to have on hand as a resource when you study for semester exams.

Learn to use your calculator: Many students barely know how to use the calculator. Look up the user's manual online and practice doing the things you need to do. Ask a highperforming student to give you some tips. Calculator skills make homework and testing more efficient and more accurate.

Form a study group: Some students learn better in groups than by themselves. Don't let it be primarily a social group, but a little socializing might make it fun and thereby motivate you. Also, in a group different people understand different concepts, so chances are one person can explain it to the others.

Follow principles of effective testing: There's a lot to say about this tip, but the basics are keep track of the time, don't get stuck on one question, and use all the information on the test to help you.
Good luck!