The law of attraction became really popular after the movie "The Secret" in 2006. This had a huge impact on the world and I believe people love the idea that you can attract good things into your life. I loved the movie, and have read the book many times, but there is still a lot of confusion about how to actually apply it.
1 - It's about Vibration NOT thoughts
The main idea is that people manifest their reality not through their thoughts, but through their VIBRATION. The Universe responds to the energy you generate by your thought, as opposed to the actual thought itself.
So if you are thinking about your goals, but feeling frustrated that they haven't appeared yet, you will attract into your life more things to make you FEEL frustrated.
You need to get yourself into a good vibration before you can manifest the energy of what you really want. This can be anything, and will totally depend on you. For me, I like to put on some music and dance. As long as it makes you feel good then it works.
2 - Let go of Resistance
Many people resist good things that come to them without even realising it. This is because you have created an image of yourself based on your current problems or circumstances. You believe that you are unlucky, or money never comes to you, or you always get bills, or you never find love. Then when money, or love, or luck comes to you, it is at odds with your identity, so it is resisted.
We see this in people who win the lottery, only to find themselves broke again a few years later.
You need to create a new self image to match your new reality, and let go of attachment to your former or current situation, otherwise nothing will change.
3 - Don't get hung up on the details
It is important to get an image and feeling about what you want that makes you feel good. But where we fall down is getting hung up on the details of how it is going to happen. There are countless ways that your dreams come true, and we never know exactly how until AFTER. The more precise you are on how it is supposed to manifest, the fewer ways the Universe has to give it to you.
There are millions of ways to get rich, but you can maybe only think of 2 or 3 methods which would involve years of work. Consider the fact that every successful person has started off with a general idea, but then have innovated and adapted as new opportunities came along.
So get happy, be positive about the future, but don't get too precise about how it will materialise.