Your students are waiting. The first class of each session is important to allow and encourage the students to get to know each other.
As important as a love and interest in fencing, social ties are often what brings people back to the salle.
While waiting for latecomers, I like to start with short history lesson, and a brief explanation of the three weapons.
On to the floor for a brief warmup. Warmups are important, not only to get the students physically prepared for the exercise, but they also serve as a psychological break from the mundane world to the world of fencing. (They also allow time in class for stragglers to arrive.)
Next comes a footwork session. For the first lesson, I begin with showing a proper onguard stance, describing each of the various elements (foot orientation, distance apart, arm attitude, etc). The students then begin their actual physical introduction to the world of fencing by attempting to contort their bodies into an onguard stance.
Onguard is followed by advance, retreat, distance, and lunge. (Whew!) During this time I will circulate and try to make simple corrections. Don't get too particular at this early time. They will learn and progress with time.
At this time, a break is called, and the students are given a chance to dress for the first time. I frequently will only have them draw weapons, gloves, and a mask. This can take some time so schedule for it. while they are rummaging for the proper sizes, safety is addressed (i. e. no blade work without masks, etc.) Once the students have their first layer of protective clothing, it is time to take up how to hold the weapon properly. First, I'll demonstrate, then have them follow without gloves, then with gloves. I take some time with this, as proper grip now prevents trouble later.
Back onto the floor, where we will go through a simple salute, and then through onguard and the footwork holding the weapon.
Finally, equipment is put down and a minibrief warm down stretch before sending them on their way until next time. I will encourage them to arrive early and draw their equipment before hand soas to not cut into class time.