Here's the most important one:
1) If the situation has escalated to tears (the child's or YOURS), take a break. Once things are this hot, not much concentration or learning can occur. (Of course, if the tears are fake and produced just to get out of doing the homework -- leave the room and make him tough it out!)

2) Keep in mind that math can be one of the most frustrating things on the planet. This is triply compounded if the child does not have a strong enough foundation in the topics building up to the task at hand.

3) Referring back to #2 on my list: When helping, try to identify if the difficulty is with skills that the child should have already mastered. If it is, then your energies are best spent in reviewing. The child will not be able to move forward if the foundation is not there.

4) Let the child know that you understand their frustration... BUT don't feed it! Don't say things like, "Oh, I know. I hate math too!" You can, however, say something like, "I had trouble in math too. But I wish I would've stuck with it better than I did."

5) If the child has procrastinated and is now trying to do his homework at the last minute - and trying to make everyone in the house suffer with him... It's cruel, but let him suffer alone. Even if it means that he will not get it done and his grade will suffer. Rescuing the child who has procrastinated will only cause him to do it again and ASSUME someone will bail him out. This is not a good view of the world to develop.

Here's an easy example: If the child cannot do long division because he can't do the subtraction part... Then a review is needed.

Here's a list of questions you can ask the child when they are stuck:

1) Is there an example in the book like this?

2) Do you have an example like this in your notes?

3) Can you do some easier problems and go back to this one after?

4) What part of the problem is giving you trouble?

5) Let's read the problem together and make sure we understand what it is asking.

6) Can we draw a picture of the problem? (This works well for word problems.)

7) Can we make up an easier problem that is similar to this? Then we can work our way up to this one.

8) What did your teacher say about this assignment?

9) Why don't we take a 10 minute break and come back to this when we aren't so frustrated.