If it's your first ever flight. i.e. a trial flight.
I'd expect you'll be shown around the plane during the walk around with explainations as to what is what etc.
A good talk about the instruments and controls. You'll run through the checklist with the instructor and may be given the opportunity to taxi to the A1 hold or Charlie hold with a stop along charlie to do power checks.
The instructor will handle the radio. You may or may not get to do the take-off. S/he will tell you to apply full throttle. Most likely explain what s/he is looking for as you hurtle down the runway, temperatures and pressures ok, full power, and airspeed is rising. S/he will then tell you to gently pull the control wheel.
Dependent on weather and where you live you may be asked if you'd like to fly over your home, or somewhere else.
You'll be in comms with Tower, then change to Approach on the climb out. Most likely report at Sevenoaks.
For the most part a trial flight is purely for you to get the experience of flight and to see if it really is something you want to do. You'll get to control the plane for the majority of the flight, but it won't be a 'lesson' as such.
Who are you flying with? What time is your lesson booked?