Sixthsense

Ok, so I was working on some multiple choice problems and free response questions that were dealing with slope fields. My first question is what exactly do you usually do when you are presented with a slope field and must pick the correct value of dy/dx.Do you select random points and pug them in and see if the y match or is there a more efficient method. Also, I was wondering on the free response how you differentiate between close slopes, like 3/2, and 2, when drawing a slope field.

Thanks