Re: how to host a t-shirt graphic design contest
Basically you figure out the exact prizes, write up the rules (who's eligible, who's judging, who owns the copyright to the designs submitted even if they don't win, legal mumbo jumbo, etc.), put out the call for entries. Promote the call for entries and the contest. Judge the winners (or start the voting process) and pick a winner and give them their prize.
Also be aware that there will be some graphic designers that will be upset with you for holding a design contest because they liken it to asking for free work with no guarantee of getting paid.
There are many ways to do it, but you'd probably want to put up a web page to make it easier to collect entries.
Basically you figure out the exact prizes, write up the rules (who's eligible, who's judging, who owns the copyright to the designs submitted even if they don't win, legal mumbo jumbo, etc.), put out the call for entries. Promote the call for entries and the contest. Judge the winners (or start the voting process) and pick a winner and give them their prize.
Also be aware that there will be some graphic designers that will be upset with you for holding a design contest because they liken it to asking for free work with no guarantee of getting paid.