Now THAT is my kind of question. I teach preschool, and on Sundays, I teach 3-4 year old Sunday School.
First thing, you need a co-teacher. Without another adult, it is less likely you'll be able to get off on the right foot with a 14-1 ratio. If one kid is in meltdown, you can teach, and the other person can take that child out of the room. If three kids need to go potty, the other person can take them while you teach. Also, while you're doing circle time with the bible story, the other person can be setting up the activity at the tables.
Next, have confidence. Come up with a routine, and rules/boundaries, and stick to them with assurance and authority. Stay calm at all times -- it will make you more powerful and authoritative than if you lose your cool, in which case the tantruming (sp?!) child will have all the power.
As I said, come up with a routine, and stick to it. If your routine needs adjusting after the first day, then go ahead and change it, but try to start doing things the same way each Sunday, as soon as you can. Children find routines very comforting. They know what to expect, what happens next, and it both lessens their anxiety, and makes them feel more confident, because *they know what to do*.
In my class, the kids come in and put a sticker on the attendance chart, while I greet them and the parents. Then they have a quick activity to do as other kids arrive (either sitting at the tables to color the day's story book, or going around the room looking for the hidden cards that match the ones that they are holding). When everyone has arrived, I turn off the lights to get their attention, and give them the two minute warning, and "please finish your work." Then I turn off the lights again, and give clean up instructions -- where to put everything, and then where to go next (the carpet for story time). If kids talk or ignore me while I'm talking with the lights off, I redirect them, and wait until everyone is quiet. Then we have story time, and we do it the same way every time (prayer, each person says something that happened to them that week, and we all read the bible story in our little storybooks). Then I dismiss the children one at a time to go do the activity. I tell them I'm looking for people who are sitting quietly with their legs crossed, and hands in their laps. They all want to be chosen, so they get really quiet.
Think through every moment of the morning in your head beforehand, and question yourself about what might happen. If we're going to the tables, or getting in line to go explore the church, I don't send the whole class at once, or they will run and push. I call them to line up one at a time.
Also, practice some songs and fingerplays you can use to get their attention. I call kids to come sit down after clean up, and then if they are stalling, will start doing a fun song/fingerplay with the kids who ARE in the circle, and the rest get interested and hurry to join us.
Forgive yourself any meltdowns or messups, and see each difficult moment as an opportunity to learn. Enjoy the wonderfulness of preschoolers. Your concern about how to start the year off right leads me to think that you are a thoughtful, caring person, and THAT leads me to think that you WILL start the year off right. Have a great year!