1:
First off, congratulations, great job. Take bow and a victory lap.
2:
Second, decide if you want to judge or not - if you don't want to, let the thread you won in know, the runner up will judge, and so on down the runners up, as decided by the previous judge.
Judging can be time consuming and difficult, although you shouldn't let inexperience or worries about "not being good enough" at the game be deciding factors - your contest & judging should be about what
you find interesting about Dominion, and that's for you to decide.
3:
Come up with an idea for a contestIf you're stumped, there's a thread of
not-yet-tried contest ideas to pull from, and a
list of previous contest ideas; try to not do a repeat that we've done in the past 50ish contests (a year or so).
You may want to disqualify things that are difficult to judge like Traveller lines or fan mechanics; or disqualify previously entered entries; or disqualify things that don't fit the prompt - that's perfectly reasonable; You can also say "hey I won't disqualify any entries, just try to make them match this criteria", and that's fine too. It's your contest for that week. You can either require or waive that people include an image in their submission - it makes them a little harder to miss when judging - but this does make it more difficult for mobile-only users to submit cards.
4:
Make a thread about it in this WDC subforum.
The mods will sticky it. Include the contest number, a brief description in the title, and the longer description in the body. The mods may fix minor format tweaks. It's fine to let your contest run a little longer/shorter than a week, just try to announce that beforehand.
5:
Check in on the thread periodically if you're disqualifying entries, or you can be a little more lax if not. Try to give a 24 hour warning on judging and remember to close submissions before "judging" so no one ends up with hurt feelings on a last minute change. Double check your thread and make sure you haven't missed any entries - that always stings a bit for the person who gets missed during the judging.
6:
Judge the cardsThis can be meticulously detailed like Carline's judging in
contest 80 or as lax as the judging in the early days of the WDC thread - again, it's your contest. You're welcome to judge on balance from playtests, etc, or just make an educated guess, or whatever.
7:
Decide on the Winner, Runners Up, etcThe winners and runners up will go in the
hall of fame thread (you can put them there, or someone else will, that's no biggie), the honorable mentions and rest will just live in their original thread. You did it, you judged a contest, and now next round isn't your problem anymore and you get to make entries again.
Don't worry about this taking a day or two to do - it probably shouldn't come immediately as the contest closes. This may make it so you've been the judge for longer than a week - that's not a big deal.