For starters, read "Grid Systems in Graphic Design" by Joseph Muller-Brockmann and "The Elements of Typographic Style" by Robert Bringhurst.
After that, practice all the time. Do a ton of self-initiated projects or design for friends pro-bono. Always be looking at designers who you admire and figure out what about their work is so admirable!
After that, practice all the time. Do a ton of self-initiated projects or design for friends pro-bono. Always be looking at designers who you admire and figure out what about their work is so admirable!