I've always said the most effective tool a sub can use is learning the names of the students. Seating charts are invaluable in helping with this, but if the regular teacher doesn't supply one, you can pass a sheet of notebook paper around and create your own.
I once had a middle school class that would not stop talking and kept getting a little louder as class went on. I finally stopped talking completely and began writing the names of those talking on the board. With each name I wrote, the class became quieter and quieter. By the time I finished, I DID have pin-drop silence in the room. One student "What does that mean if our name is on the board?". I answered, "You'll find out on Monday, when the regular teacher returns." The pin-drop silence lasted for the remainder of the class.
As a teacher, I would often like my classes to have pin-drop silence, but I know this isn't a very realistic goal and may not be the most productive either. Kids naturally want to talk and socialize. You can't let it get out of control, but you also have to choose your battles. So I will usually let them discuss the work and help each other, as long as the talking is kept to a low level.
It used to really bother me that the children would be noisy and disrespectful while I was teaching and then would quiet down when a staff member would walk in. I said to myself that it's because I was a sub.
Then I did some reflecting and decided it was me. I never went over my rules and expectations, so the students just did what they liked.
I'm currently a substitute teacher, I've only been doing this for a month and a half, and I often ask myself what are some viable reasons to call administration. For example, there will be times when more than half the class will not be sitting in their assigned seats, off task, and chatting. Would this be a frivolous reason to call admin?
I know that if I go in there and try to get them all to change seats it will take all class period, and all them will say ,"our teacher isn't strict on the seating chart." While I do this I will just be contribute in disrupting the students who are there to learn; who have their hands raised; who need me to assist them with their work.
However, I find it's easier to control students if you are subbing for the class for more than a day, or if you are in a classroom where there desks sit individually, and the assignment is something like a read around.
I don't usually require pindrop silence. I do require that they do not interrupt during direct instruction, and that there are certain times during the day when it will need to be silent, such as during a test or silent reading (depending on grade-level... for instance, 1st graders don't usually internalize their reading very well, so I just require very quiet reading). I explain the need for silence, and that they will be silent for x amount of time, and that I will let them know when time is up. I frequently walk around with stickers, which I put on the back of the hand of those who are being totally silent. I'll usually comment something like "Great silent reading" and make a show of putting on the first 2 or 3. It's amazing how the talkative students will suddenly be super-silent readers when a sparkly smiley face sticker is on the line. I almost always end up with everyone in the class having a sticker, since I'll make a second round to get those who have caught on. I try to work discussion and quiet talking into the day so that when I do expect complete silence, it's not like they've been having to do it for hours on end. That will only lead to rebellion (which I discovered the hard way my first month subbing). While I don't expect complete silence all day, I do make it clear to them right at the beginning that they will be permitted to talk at SPECIFIED times throughout the day, and that they WILL NOT be disruptive or get the noise to a volume that will bother anyone in the hallway or any other class. and that if they do, they will lose talking privileges for the remainder of the day. I usually follow that with, "But I know that this class would never do that. I'm sure we'll be just fine with talking at a quiet level today."