If you want to do anything more advanced with Fritzing — design your own footprints, use custom-shaped PCBs, panelize your designs, etc. — you are going to need to edit SVG files. Fritzing itself doesn't let you do that — the authors figured out that any crippled editor they can make will be infinitely inferior to the general-purpose graphics editors made by dedicated teams. So they rely on you using an external editors. Inkscape is one particularly nice graphics editor that edits SVG files natively and lets you do a lot in a very convenient way. It has grids, rules, automatic arrangement of objects, measuring and even lets you edit the XML attributes of elements directly. So the very first tip I have for getting the most out of Fritzing is installing and learning to use Inkscape.