I usually recommend starting small. In a blog post of mine (located here) I talk about starting with a goal of making just $10 a day - if you're less experienced with how the internet works, that could be even less. It's best to aim, at minimum, for enough to cover your costs. (Domain names, hosting, etc.) Some example methods of making money are GPT sites, affiliate networks, paid reviews, and more. People are also free to explore the option of starting their own services such as content creation, social bookmarking / directory submissions, etc.
The most important thing to do is never give up and continue to put in a lot of hard work and effort (read more here) and if you want to continue making money to invest the profits back into the business.
Let's imagine you live here in Pennsylvania (United States) where minimum wage is 7.15, if you manage to get a part-time job (25 hours a week) and work for 52 weeks (1 year) you will have made approximately $6,500 after taxes. This doesn't count other expenses such as eating your lunch, paying for fuel to drive to work, anything such as uniform expenses, etc. If you make $10 a day online for a year, you'll make $3,650. Interesting, right? So imagine if you were to step up the process and make 20$ a day - or more!