When drawing using a grid I will photocopy the work I am trying to recreate and actually draw the grid onto the copy. That way I can size up the work I want to copy if I have to to get the little details.
Guide Note: this is a great way to preserve your original. You can also do multiple copies - doing the maximum enlargement on the photocopy, then doing a copy of that copy - you can always trim the edges and stick the pieces together. This is handy for scaling up sketches for painting, as it is difficult to go from a very small grid up to a very large one accurately.