Step 1 -- Assess your body
This may require a tape measure. Measure over the center of your bust, the largest parts of your hips, your waist and your leg length. In your measurements, take note where the largest areas of your body are. Are the numbers very different, or close? Note all of this.
Step 2 -- Make a sketch
Yes, this means make a drawing of yourself. Grab a pencil and some paper. Using the numbers found by your measurements, make a scale sketch of what yourself. This will aid you in comparing and deciding what general body shape you are.
Step 3 -- Compare
Read through the list below and decide what body shape you are. Follow the link to learn more about dressing your figure.
Your hips is your largest measurement. Your waist is smaller than your bust.
Your waist is your largest section, close to your bust and hips. 
Your waist is your smallest section. Your bust and hips are close is measurement, and larger than your waist.
Your bust is much greater than both your waist and hips.
All your measurements are very close. There is no defined waist.
Your height is under 5'4.
Your height is over 5'8.