Language is important
A well-written problem is stated in precise language. The words and the symbols work together. Remember that you must communicate in logically written, carefully thought out prose. Try to connect your equations with sentences that lead the reader through your argument.
Don't Generalize too Soon
If you're trying to prove something about prime factorization make sure you factorize some numbers and examine them closely. Don't be too eager to make general, symbolic statements until you've examined specific examples carefully.
Solve a Simpler Problem First
Sometimes you can state a simpler problem that is easier to solve than the one you're really interested in. The simpler problem may give you insights into how the more complicated case will work.
For example, if you're trying to prove a statement about 6-digit numbers, why not consider 4-digit numbers first? If you're trying to solve a big polynomial, try a smaller polynomial first.
Leave it Alone
I have frequently found that an intractable problem often benefits from a good night's sleep. Leave it alone, come back a few hours later or the next day, start fresh and think differently.