Water down a bit of gesso primer so that it isn’t too thick, then apply to the surface of the lino with foam brush (ideally) or a soft, wide brush. It needs to be very smooth so that there are no raised streaks for your pencil to trip over or so your transfer doesn’t distort. Leave to dry.
Transfer your image or draw straight on to the dry lino. I have drawn the same image in pencil on a piece of lino with gesso (right) and without (left). As you can see, the image is extremely clear on the lino with the gesso.
A general tip is to make sure your lino is warm; you can place lino on the radiator or use a hair dryer.
Gesso is waterbased so when you are finished you can rub the primer off with a damp cloth.