It's important to sketch out your ideas. It doesn't matter if you can't draw... just as long as you can visualise the look and shape you're after, and the type of fabrics and colours you want. Remember to take care to pay attention to all the details such as types of button and possible gaps in splits or plunging collars.
Take your time choosing the right fabric so that it reflects your story and has the right feel and movement. If your design has any special requirements, such as stiff elements, opaque areas in transparent designs or special adhesive tape for modesty, then make sure that you note it down on the drawings. If possible, attach several samples of fabric (swatches) to your drawings.