For folks who won a contest for the first time: Step by Step rundown of the sequences [View all]

These are basic guidelines, nothing is etched in stone, I may be forgetting something, but they may nevertheless take the edge of wondering how to proceed, or as I did, panicking.
The host or hostess is in charge, all decisions begin and end there, and so not much is to be feared

Announce the theme in the Photo Forum - as well as the schedule for submissions and voting - give at least 1 week between announcing the theme and the start of submissions, for people to go out and shoot.

Start submission thread in photo forum, along with a separate comment thread, link them to each other and caution folks to not make comments or ask questions in the submission thread. If they do anyway, just cope with it , remember, nothing is etched in stone.
Into the header of the submission thread copy and paste the basic rules about photo submissions.
there is a pinned thread at the top to the photo forum, by CC, “Preliminary or the Gathering of Contest Rules”
where you can get the info about all of that

During the submission time host or hostess needs to remain vigilant to questions or problems that arise, and at times remind folks of the timing to submit. One tries to make noise so those who want to enter a photo don’t miss the fact it is happening. Many a host or hostess also post a notice in the Lounge to solicit photographs.

When the time comes to make the polling threads, decide on how many threads are needed based on the number of submissions received. 10 is the maximum per thread. I like to have one third or thereabouts of the submissions in the finals. So for example when it is 21 entries, I like to have 7 finalists, and they will come from 3 polls of 7 each.

I am not going to explain here how to make the polling threads, there may be instructions about that somewhere already, and I am not the best at this anyway. Just gather the links of the submissions as they come in and study old threads. You can always ask along the way.
Make the threads and explain the theme to the voting public, you want them to know what they are looking for, not just have them vote for pretty pictures. Again state the timing involved for how long the voting will be, also tell the photographers how you will chose the finalists, and how many there will be. Post them. Link them to each other so folks can go from one to the next and vote.

Then you are almost home free, the most difficult is behind you.
The next step its to gather the finalists, run a poll if there is a tie, or flip a coin, or make the choice any old way you want. Remember: you are the boss of this.

Run the finalists along with the same explanations of the basic polls about theme and timing.

Announce the winners and pass the baton.

Hope this helps.