I did viewings myself.
I totally agree, first of all show them round and then let them go round themselves.
Also, spell it out that you are going to do this beforehand so they know what to expect.
A great tip I got - and which works well for covid, handily - is to let them go in the room first. Walk past the doorway, then invite them to go in. You don't even need to go in the room, you should hover by the door.
This is important for two reasons: it makes the room seem smaller and more cluttered if you're all in their together. Also if they walk in first, they can see the rooms properly without you in the way.
Also for each room, think of a selling point you can tell them about, so you're not just stating the obvious e.g. "this is the kitchen"
Instead, perhaps say something that's not obvious from looking or which suggests how they might use it.
For example "the sun comes through this window in the morning, it's a lovely light".
Or, in the kitchen "this boiler was new just a year ago" or "we have these french windows open a lot in Summer, we like to eat out in the garden on summer evenings. This part of the garden gets the evening sun and is totally private."
Or "we've got a single bed in here now but we used to have a double here, there was plenty of room for it".
Maybe write your notes on a piece of paper, if you forget things in the heat of the moment like I do!