An excellent way to learn more about machine learning is by trying out a competition! Kaggle (http://www.kaggle.com) is a marketplace of ML competitions and was already mentioned in the introduction. On the website, you will find several different competitions with different structures, and often cash prizes.

The supervised learning competitions almost always follow this format: you (and every other competitor) are given access to labeled training data and testing data (without labels). Your task is to submit predictions for testing data. When the competition closes, whoever has the best accuracy wins. The prizes range from glory to cash.

Of course, winning something is nice, but you can gain a lot of useful experience just by participating. So, you have to stay tuned after the competition is over as participants start sharing their approaches in the forum. Most of the time, winning is not about developing a new algorithm, but cleverly preprocessing, normalizing, and combining existing methods.