Any of the "standard" solid fuels will work coal, coke, charcoal or corn. With coal make sure it is a nice deep fire (about 6") so you end up with a ball of coals about the size of a grapefruit and the piecesa are about 1' in size and keep feeding coal in slowly from the sides so you have no raw coal in contact with your steel, it does nasty things to steel when it releases the volatiles. The coke fire is much like a coal one, keep it deep, but it is harder to start and needs a constant supply of air or it will go out. Its good point is that there are no volatiles so it does not make smoke or smell and is easy on the steel. With charcoal, make sure its real charcoal, not the BBQ briquettes they have a lot of additives in them. The charcoal fire does not need so much air and you need to keep your extra fuel away from the fire or it will burn up without an air blast. It still needs to be deep or you will be in the oxidising lkayer all the time. As for corn, it works well and is easy to get but you go through quite a lot.
In all cases when the fire is going control the edges with a sprinkle of water occasionally.
Above all, have fun and keep safe.