Clear out all the ash from the pan and the griddle
Add a load of scrunched up newspaper – tear each sheet in half, scrunch it into a ball add one layer of these
Add locads of kindling – a layer at least as thick as the newspaper. Make sure it’s very loosely packed so the air can circulate
Open the LOWER vents on your fire. Not sure about top vents, it’s 20 years since I lit a coal fire, but open them if you have them
Light the paper, when the kindling is roaring (5 minutes or so) then add half a shovel of coal
when the coal gets coing, add a little more
close the top vents when the coal is burning nicely, then use the lower vents to control the fire. Make sure you empty the ash regularly, and check the griddle for clinker (fused ash)