LaTeX in a Minute: No more preamble (sort of) 

1. Create "YourFileName".sty
2. Type into .sty file:
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{"YourFileName"}
3. Cut and paste preamble from .tex file into .sty file (leave \documentclass[...]{...} )
4. Type \usepackage{"YourFileName"} in main .tex file