After seeing so many...misguided thoughts about what magic is and how does it work and "why my nursery rhyme didn't turn my stepmom into a toad" thing, I thought about posting a bit about the Laws of Magic
Firts of all, Magic is based on 2 general principles: The Law of Contagion and the Law of Similarity
The first one states "two things that were once connected retain this link and have the ability to affect their supposedly related objects, such as harming a person by harming a lock of his hair"
The second one, also called Homeopathic Magic operates upon the premise that "like affects like", or that one can impart characteristics of one similar object to another
This being clear, I want to make reference to a few texts: The Emerald Tablet and the Kybalion. These two texts give a lot more insight on the way the Universe work, and magic works with the universe
Actually magick is based on more than two laws. Honestly, I don't see these principles as Laws, but something good to know. And you can't say a few words to turn someone into a creature that they aren't. Maybe one day, science will do that, because they are thinking of toying with the DNA of sailors so that they are part fish, and to breathe underwater. Their reason for this is that they want to stop training dolphins to go underwater to fix things. My point is, you simply just can't chane DNA with saying a few words.
Some of these laws were restated ideas of the Pyramid of Manifestation. The Pyramid of Manifestation consisted of some important laws of magick.
Law of Contagion
In magick, it is assumed that you can effect a whole by using its part. For example, like you said, physically you can hurt someone with a spell by using a part of them--hair, blood, nails, saliva, etcetera--to effect the entire person themselves. It's just like saying how a giant asteroid hitting one part of Earth can destroy all life on the planet; asteroid is somewhat part of life and it destroyed all life on Earth.
The Law of Contagion doesn't just work physically, but contagiously--the way you can catch an illness. As you may know, contagion means "the communication of disease from one person to another by close contact." For example, if you hang around a powerful person, you can catch their aura of power. If you stay around a healthy person, you may become healthy yourself.
Law of Cause and Effect
From every action, there is a consequence or a reward. After doing a spell (an action), you can get a consequence and/or a reward, depending on what spell you casted and what kind of outcome you are expecting. For example, say you casted a spell for someone to love you (action). You may get what you want, but some one will hate you (consequence).
Law of Knowledge
To be effective in spell casting you must understand what to do to lead yourself into success or failiure. Knowing your requirements for the spell/ritual will help you lead to your goal/intention. For example, if you used herbs, candles, or incenses and didn't know what they were for, you may possibly fail. Knowledge will help you, in magick and in life.
Law of Self-Knowledge
Knowing yourself and your goals will also help you succeed. Set realistic goals, and make yourself a list of strengths and weaknesses can help you lead to a goal also. Just remember that your goals, heart, and mind must work together to succeed.
Law of Assosiation
Have you ever heard the quote, "you are what you eat?" This quote is very similar to this Law. Eating unhealthy food (foods full of oil, grease, fat, sugar, etcetera) will make you healthy, and eating healthy food (fruits, vegetables, low-sugar, low-fat, etcetera) will make you healthy. Well, in the Law of Assosiation, you can take the qualities of something you want by absorbtion. If you want to be smart, be like a computer--take the qualities of it; be fast, "programmed," knows almost eveything... You get my point. As long as something that has a quality is close to qualities you have, then you're good. For example, you can't be a bad singer and want to be a good singer; for that you'll need practice.
Law of Similarity
Like BFearn has said, one can impact something else that has similar characteristics. They can also act as a subsitute for something/someone else. For example, in healing spells you don't always have to have the person physically withy you, but you can have a picture or a poppet.
Ah well, yes, you can infer more laws, it depends on the author and your personal veiws. For my part, I used James Frazier's "The Golden Bough" (A must read book for anyone interested in magic), which are the two basic principles of magical operation according to most western esoteric schools
Now, about those you mentioned, I can argue.
The Law of Cause and Effect, as expressed in the Kybalion, is more an universal principle, not specifically a Law of Magic, which was my whole point here.
About Knowledge and Self Knowledge...well, I can't help to disagree...even if a magical operation is performed incorrectly, it won't just "happen nothing", in any case, there will be some sort of backlash to the operator, meaning the energies did get notice of the ritual and since it wasn't harmonic, well...you might get what you asked for, but it will be tough...now, the self knowledge...not really a law...in any case, I'd call it the Law of Common Sense..something rare to find these days...however, it seldom happens that magic works in unexpected ways, and, in my experience, despite my belief (or lack of thereof) in the success of the operation.
These were just "laws" I studied from the past and wrote about in my computer. I also disagree on these Laws, because they kind of don't even sound like laws...but I agree with you, and as I wrote earlier, these are just some of the laws I studied in my past.