Zubrin has done this all for you (Score 3, Informative)

Have a look at 'The Case For Mars' and 'Entering Space: Creating a Spacefaring Civilization' by Robert Zubrin. The first bascially explains step-by-step how we can use present-day tech to send humans to Mars within a decade and goes on to explain how it would be possible to terraform the planet with Martian natural resourced etc. The second book reaches out further, exploring the idea of using Mars (for example) as a stepping stone for missions aimed outside of our solar system.