[tensafefrogs]

Start with the basics of data structures and algorithms. Get a textbook and read it and implement the structures using whatever language you like, and find problems that are solved by using those data structures (and solve them).

Watch computer science lectures on iTunes U. These days all the top schools put their lectures online. Try to do some of the homework assignments. If it's too hard, figure out what part you don't know and find an online course on it. Then try again.