If you're like I was, when you think about positive affirmations and that sort of thing, you probably think, "Bullshit!" I thought that for a long, long time, until I gave it a shot and now I swear by them.
What is a positive affirmation? It's a short phrase, basically, that's positive, that you repeat when you need something. For example, "I will feel great today!" or "I will not be late!" You can't just repeat the phrase over and over with no emotion, though. You have to believe it's going to work and that what you're saying is true. Funny story about the first time I tried it:
I was running late for class one morning last winter. I was looking nervously at my clock in the car and I just started repeating, "I will NOT be late and I will find a good parking spot!" I repeated that the whole 15 minutes to college, when I only had about 10 minutes to get there. When I pulled into the parking lot, I still have 5 minutes to make it to class and I got one of the first parking spots (at the very end of the row, close to the building) in the student lot. I walked into class with a minute to spare.
I thought that was just luck, though. But, I started repeating things like that all the time ("I will not fall down my icy steps!" "I will find a bra that fits!" "I will sleep well tonight!") and they were all working. It was crazy. This stuff goes hand in hand with the Law of Attraction. Basically, you attract what you focus on. If you focus on negativity, you'll attract it, and that goes for positive things as well.
Give it a try sometime and see how things go.