Inkscape is the open source svg tool of choice. I'd advise version 0.91 rather than the latest 0.92 as they changed the pixels per inch in 0.92 and that has caused me some grief in Fritzing sometimes (but not always) and parts creation is hard enough without tools screwing you over. These are the two latest tutorials I'm aware of (both in the forum here):
When you have problems (note I didn't say if 
) post here, preferably with the fzpz file or svg file of the part giving you grief and a number of us will help you out. We need more people making good parts so help to do so is available.
Peter