When working a story problem, use these four steps as a guideline.
Write a good definition statement. You should define all variables used in the problem. It is usually better to let the initial variable be the smallest quantity or the one that all others are defined in terms of. The reason the smallest is the best is because everything else will be in terms of addition and multiplication, instead of subtraction and division. Some instructors have been known to give no credit on the problem, even though the answer may be correct, if there is no definition statement. And yes, these instructors are still teaching here, so be careful if you go on to another class. Get in the habit now.
A good definition statement often involves more than writing down "let x be the first number and y be the second". For example, if one line of the problem says "twice the larger is three times the smaller", then you should define the variables in terms of the size: "let x be the smaller number, let y be the larger number". This will help later in the second step.
Another thing to watch out for is consecutive integer problems.
Write one or more equations describing the problem. Since you defined all of your variables, this should be easier. If the problem says "twice the larger is three times the smaller", you don't need to worry about getting the variables right because you defined them properly in the definition stage. Using the good definition statement above, this becomes "2y = 3x".
Solve the equation(s) arrived at in the second step. Write down the answer in terms of the original problem. "A story problem deserves a story answer". I have known instructors who have taken off points if the answer isn't a complete sentence. And yes, these instructors are still teaching here, so be careful if you go on to another class. Get in the habit now.
Check your answer! Not necessarily into the equation(s) arrived at in the second step. You may have solved the equation that you have correctly, but had the wrong equation to begin with. By checking into the original problem and asking yourself if your answer makes sense, you can avoid some simple mistakes.
Let's examine a story problem and some common answers and why the answers don't make sense when checked.
Billy can paint a wall in 5 hours and Suzie can paint a wall in 4 hours. How long will it take them, working together, to paint the wall.