Necessary Background : Mathematical Physics, Quantum mechanics, probably quantum field theory/Particle Physics for the later parts. But, more than anything else, interest in symmetry groups and topology as they enter into physics.
Link : from http://physics.harvard.edu/~dtlarson/tutorial05/
Groups, Symmetry, and Topology
Comment : This is a collection lecture notes written in a kind of no-nonsense approach. Contains a short intro to Lie Algebra, its representations and stuff. Do look at the list of books provided at the site linked above !
Posted By : Loganayagam.R.(Tom)