When drawing I try to make the value the shade I really think it is. At this stage I tend to be too light overall. Then when I thought I was finished I realize that the values are not dark enough. I then look over everything again and go darker and then darker and darker.
I realized after a number of drawings that I had done what books talked about, starting from light and going darker. I didn't used to understand what they meant or get how to do it. I still don't know how to plan it out, for me it is just how it unfolds. It is not that I'm afraid to go heavy and dark it's just that I don't yet have the skill to lay it down so accurately at first. I am just learning so I take it lightly and it's easy for me to go in darker.
I don't like the make it dark and erase back method of drawing. I only do that when it's by accident or a mistake or if the pencil is too thick and unintentionally colors in an area that I wanted bright. If you are going to do a lot of erasing I have learned you need to use a high quality paper so it will cost you more money.