In storing coal, it may be wise to remember that coal is subject to spontaneous combustion. I think there was a thread several years ago where this was discussed.
Unlikely to be a problem for amounts likely for domestic use, but yes, still take care.
Coal when exposed to the air very slowly reacts with oxygen from the air to produce carbon dioxide and heat. Under most conditions this heat is removed by normal air circulation and no undue temperature rise is produced.
In the case of a sufficiently large coal pile the heat can not be removed and the interior of the pile becomes hotter, thereby accelerating the reaction and producing more heat and eventually fire.
When the fire is confined to the interior of the coal pile it burns very slowly due to the limited air supply and may not become obvious until the pile is disturbed. Exposure of the very hot inside of a slowly burning coal pile to fresh air may result in a fierce fire.
Risk factors that tend to promote spontaneous combustion include
Very large coal piles
High ambient temperatures
Coal dust or very small coal in the pile
Damp.
Left undisturbed for a long time.
If a coal pile becomes unduly heated within, but is not actually burning, then the coal should be spread out over a large area to cool it. A mechanical excavator or similar machine will probably be needed. Fire fighting equipment should be to hand.
For safe storage of a few tons up to a few dozen tons, I would proceed as follows.
if the coal was purchased in small bags on pallets store it thus, but do not stack the pallets atop each other and allow a free air space on every side of every pallet.
If the coal came in one ton bags, keep it thus but not stacked and with a free air space on each side of each bag.
For small bags stacked by yourself, stack in such a way as to leave plenty of air spaces within the stacks.
For coal tipped loose, pile it as convenient but avoid more than 5 tons in one pile.