There’s a balance you have to find between too much white (negative) space and not enough. Some images you should fill the frame. It’s good to experiment with both; take a photo of the same subject with no background (even cutting into the subject), one with very little, and one with more background. Have others critique this in class. Keep in mind in your composition, try to stick with the rule of thirds at the beginning. As you go along you will find good ways to break this rule.