Wicca doesn't have "laws" as much as it has guidelines or advice that most adhere to in their practices.
The most commonly trotted out as a "law" is the Wiccan Rede, but Rede means advice...not law. And indeed it is commonly only the last eight words that people know and believe when in actuality the Rede is far longer.
Another so-called "law" is the "Rule of Three" which is grossly misunderstood.
You can read about the Rede and the Rule of three at:
And there is a wonderful site with the history of the Rede and its many variations at: http://web.archive.org/web/20031218001055/www.draknetfree.com/sheathomas/index.html
Less well known are The Ardanes which come down to us from Gerald Gardner and which he says came to him from the coven in which he was initiated. There are 161 so-called laws in the Ardanes, many of which seem quite out of date today and which most pay little heed to. You can read them at http://wicca.cnbeyer.com/laws/old_laws.shtml
And finally there is the Witch's Pyramid which has to do specifically with spellcraft. The Pyramid tells us...To Know, To Will, To Dare, To Keep Silent." http://www.angelfire.com/falcon/enchanted-moon/pyramid.htm
Of all of the so-called laws that involve Wicca and magic, I would say that the Witch's Pyramid is possibly the most important even if it is little talked about in most books.