The two most important parameters for firewood supply are moisture content (degree of seasoning) and wood species (hardwood or softwood). Log size is also important.
Firewood should always be seasoned before use, usually before supply, preferably for 1-2 years, depending on when it was cut. If a tree is felled in spring or summer it will have a much higher moisture content than if it is felled in autumn or winter.
Small round wood (SRW) should be dried by stacking on bearers in a sunny place, exposed to the prevailing wind. Most moisture loss is through the ends of logs, and these should be open and exposed, but air flow through the stack should be unhindered. Bark may be scored or partially or fully removed to assist drying, and the stack should be covered to prevent direct re-wetting from rain, with either a roof, or waterproof or semi-permeable sheeting.
Logs that are well seasoned and fully air dry (typically around 25% moisture content) have cracks and splits across the grain, and the bark comes off easily.
In general hardwoods make better firewood, as they are denser and burn more steadily. Owing to the higher density, for a given moisture content a given volume of hardwood will be heavier, and contain more energy, than the same volume of softwood. Softwoods can be easier to light, however, and burn more quickly. They also tend to be marginally higher calorific value for the same moisture content owing to the higher lignin content. Softwoods can be useful for kindling.
Provided they are of suitable size to fit in the firebox, feed hopper or grate, log sizing is relatively straightforward. If larger than 10-15 cm diameter they should be split.