I think the best way to learn Spanish is to go ahead and purchase a Spanish course such as
Rocket Spanish.
I say this because although you might pick up phrases and words from
reading Spanish literature or speaking with Spanish speakers, the fact
is that you won't build a natural foundation of the Spanish language.
By learning in an almost haphazard and un-structured fashion, you are
only asking for a lengthened learning period and problems later in your
learning. This could include not being able to be "fluent" in your
Spanish because you haven't learnt the correct way to "put different
words together"
By starting with a tried and tested Spanish course, you'll be instantly
put onto the right track by a proven step-by-step guide. This will give
you a strong basis to then build your Spanish up from naturally and
cleanly.
Think of it this way - at school, you don't learn really hard words
when you're only small. You need to get to grips with the basic stuff
that makes up the language first in order to grow your knowledge later
on.
Sure, you'll pay some money up front for the Spanish course, but if you
use it right - you will learn Spanish a lot quicker and a lot easier
than without a course.
Check out more information on this and a
Rocket Spanish review at this
Spanish learning site.