All of these questions will be answered in the following paragraphs.
The Law of Attraction says that whatever you think, say, or do is where your focus is regardless of if it's positive or negative. So for example, if you say you want something than the universe aligns to make things happen that allows what you wanted to become reality. At the same time, if you say you don't want something than the universe will align to make the thing you say you don't want to happen, happen anyway. The reason is because it's what you are spending time focusing on. So if you want only good things to happen, only have positive thoughts.
To see if this is true look at your friends, your family, yourself. See how the things you say seem to appear on their own. You may say you want something to happen this weekend, and then it does. You may feel like you are psychic, or you deserved it, it's karma, or it just happened on it's own. But really it happened because you focused on it so much that it came true. At the same time look at something bad that has happened. For example, people on facebook like to post lots of bad things. Ever notice how it's the same people over and over complaining about the same things? It's because that is what they focus all of their time on, therefore, they get more of the things they say they don't want.
You can test it out by only thinking positive thoughts and see where it leads. Rather than make yourself have bad things happen to you, just notice the people around you, their thoughts, actions, words, and then see what happens in their life. Most likely if they are having negative thoughts than more negativity will be in their life as a result, not less. You can do the same for the positive people in your life.