You can resize your legend elements by double clicking and using the legend wizard. See Working with Legends . Here you can alter the spaces between symbols, text size, add borders etc. If this isn't as detailed as you would like you can always convert your legend to graphics and scale your symbols and text accordingly.
I find this is necessary if you have arrows on a line and say have >20 arrows.
It'll show up as a blob of arrows with the default legend.
What I have found to work for line symbols - although not a perfect solution is to convert to graphics, ungroup and double click on the line symbol in the legend. From there I alter the symbol as would in data view and decrease the number of arrows (from 25 to 3), however this will only show up on the layout view.