Learning about compression and tension in regards to bucking logs will help you gain a much better understanding of what to do and how to go about cutting (bucking as we call it on the west coast) literally any tree/log. Whether it's a fallen tree on your property or a windfall in the bush, regardless of what it is it's always smart to assess the scene in it's entirety to get a solid idea of what you're working with. Paying close attention to how the tree is laying like how much of the tree is resting on the ground or is it suspended in the air, is it bound up against another tree, is the root ball still attached to the ground, is there any loose hanging branches (widowmakers) hung up in neighbouring trees. All these factors must be considered when working around trees you intent to buck up for firewood or even just to clear a path for your jeep.
And lastly, it's never a race. Take your time and watch how the tree reacts to your saw, cutting too much compression wood will cause your kerf to narrow and pinch your bar.