For graphics design nothing will make you grow more than working with people to use your vision in achieving what they want. I suggest always try to layout things in pencil first. Even if you make little 1 inch chicken scratch thumbnails with squigles for what the text would be it lets you try out different layouts almost instantly and if it doesnt work as a chicken scratch sketch it probably wont work too well as a finished pieced. Working straight on the computer really slows the process and at first what you really want is get all the possibilities out there visually as fast as you can.

Also ALWAYS use a grid no matter how small or big the cells of the grid are it will immediately improve your work. Also fonts, reduce the amounts of fonts as much as possible (Each size of a font also counts). Make the difference in font sizes by atleast 3pt anything less will feel sloppy. If you make a title text size font and a body text size font it should be consistent throughout the project.

Some books you can look into:

Josef Muller-Brockman: Grid Systems

Ellen Lupton: Thinking with Type

Adrian Shaughnessy: How to be a Graphic Designer without loosing your soul

Museums also help and looking at work by people considered masters,

Hope this helps you out,

Rafi