SAFETY FIRST!
Man, that's a lot of stuff to cover but Mors Kochanski covers this very well in his book
Bushcraft.
Safety is the biggest thing regardless and for as much as I can talk, it's still too much to say here and never enough can be said about it anyway. Make sure the area is clear of anything you might catch in your swing; branches, other tool handles stupidly sticking out, kids, dogs, birdbaths (don't ask). Give yourself lots of clearance. I spilt an Ash stove-length the other day - burried the maul in a stinkin' little 8" round, raised the maul/wood combo overhead and spun the works around on the way down so the face of the poll on the maul hit first - the piece burst into three projectiles and one third of the round hit me square in the left shin. I was literally and completely incapable of coming up with a suitable new cuss-word at that moment - BUT, better a chunk of firewood than an axe or maul.
Make sure your tools are in top working order and use the longest-handled tools you can manage. Make certain the the head of the tool, at full swing's-length from your body, will not be able to contact your toes, shins, knees, etc. if you miss your target. If you use a block (unfrozen earth absorbs the too much energy), don't make it any taller than necessary - only as necessary so you don't split it when your maul goes through the round or when you miss - and you will miss. I still do. Set the round to be split toward the back of the block, so when you miss, the maul hits the block instead of swinging through to your shins as you will not be able to stop it and you will not be able to get out of the way fast enough. Don't use a waist-high chopping block. It might seem cool to not have to bend over in the final arc of your swing but it sets you up for a maul in the knee cap.
Don't muscle the tool - use speed (of the tool head) and stop before you get tired. Los off muscle control due to fatige means loss of control of the tool. Use the full arc of the tool to build up some speed - that last turn of the wrist at the end of the swing, just before the head makes its mark adds a significant bit of velocity. Don't "push" the tool handle - swing it for speed. The heavier the tool, the less speed required - or possible (per a given individual's fitness level). You're not "chopping," you're "splittig," so, if you're in the habit of "pulling back" just before the edge contacts the target - don't do that - follow through.
Remember that every piece of wood is different and will react differently. Frozen Hickory splitting sounds like bowling pins scattering on the lane. Mulberry is s booger about any time, Ash, when soaked, can bounce the maul back up head high (I mean YOUR head, not the tool head). Softer woods are not always easier to split, as they compress and absorb the energy the faces of the wedge impart, and on and on............... Work with a rythm. Steady, paced work will yield a bigger pile for how tired you are when done. If you get a particularly boogerly piece, suck up the pride, chuck it in the "specials" pile and go to the next one. Split the easiest stuff first, because if you don't, your fart-faced brother will! Oops! Sorry - flashback.
