Find a python program that does almost what you want and hack it to do what you want in a way that's maintainable, and then contribute that back. Do that often enough with enough projects that you have a portfolio of both small bugfixes and projects that you're moderately involved in.

Once you have a good portfolio, I'd try getting an internship at a software company. Most internships either come with job offers or are near-perfectly correlated with job offers, so treat this seriously.

I'd focus more on real-world coding than working through CS textbooks. Not a lot of academic computer science is really relevant to a career in the software industry. Most of SICP definitely isn't. SICP is a great book, but it's very academic.

See also: http://matt.might.net/articles/what-cs-majors-should-know/