Don't sacrifice morals for a quick buck — At the outset, you'll want to do all sorts of things to make money online, but don't sacrifice your morals for a quick buck. Not only will you put people off, but you'll lose Google's trust. You also shouldn't concern yourself with things like Adsense or other ads on a blog before you have around 100,000 visitors per day. Yes, per day.
Moreover, working online enables you to reach a wider range of people at any given time, wherever you are and at little or no cost. For example, if you write an eBook, in one month you can have more than 100,000 people reading your book from all over the world. This means that you will earn more money than you would have if you had decided to sell a hard-copy book worldwide, which can be very costly.