To go along a bit more with what ZY has said, here's something I learned a long time ago from those that mentored me.
Own your frequency/own your position, and speak confidently and with conviction.
What I mean by that is that you are the controller. Some pilots may think that you are there to serve them; that they are the one in charge, because they are flying and their aircraft is important. That may be the case; as PIC, their duty is to their aircraft. However, your duty is to the airspace that their aircraft is in, and to keep them separate from other aircrafts in your airspace. This means that you have to prioritize. If you have handled situation C to the point where you need to handle situation A, followed by situation B, but aircraft D calls in, A and B may take priority, though aircraft D may think that you're ignoring him, and tries to step in on things. Still handle your business as you need to, then address the new aircraft coming in.
You are in charge of the space they are coming in, and the frequency used in that space. as long as you know how to effectively manage your time and priorities, you will be fine. Have a listen to anyone higher up in the facility you are going to be assigned to; instructor or higher would be preferred. Listen to them, and look at how they manage their airspace, aircraft, and priorities while on frequency. That is what you are wanting to achieve.
BL.