Mathematical expressions should be centered on their own line .

  Poor example:

To find the slope of the line 3x + 4y = 24, you should change the equation into the slope intercept form of the line, y = mx + b.  Subtract 3x from both sides of the equation.  The result is 4y = -3x + 24.  Next divide both sides of the equation by 4.  The result is y = -3/4x + 6.  The coefficient of x, -3/4, is the slope of the line.

  Good example:

To find the slope of the line

3x + 4y = 24

change the equation into the slope intercept form:

y = mx + b

Subtract 3x from both sides of the equation and divide both sides by 4:

  3x + 4y =   24

-3x   =  -3x_____

Avoid having your mathematical expressions wrap to a second line.

Make sure the antecedent of a pronoun is clear.   It is better to repeat the term, especially in complicated explanations:

  Unclear:   Irrational numbers are a subset of the real numbers.  They cannot be expressed as the quotient of two integers.   What is the antecedent of "they"?

  Clear:   Irrational numbers are a subset of the real numbers.  Irrational numbers cannot be expressed as the quotient of two integers.  

Don't start a sentence with a symbol or a number.  

  Either spell out the number or rewrite the sentence.  Italicize variables.

  Incorrect:     2 is the only even prime.

  Correct:   Two is the only even prime.

  Incorrect:   c is the length of the segment.

  Correct:   The length of the segment is c.