Pre-drilled holes top my list. Blunt nails also work. The blunt nails tear their way through the wood instead of pushing the wood fibers out of the way.
Using wood that is not really old helps too. Really old over-seasoned wood will split worse than wood that has a bit of moisture still in it. This one may be hard to control.
It also helps if the wood you are nailing into is rigid and supported well. If it allowed to flex or vibrate the other wood is more likely to split.
The rungs need to have a certain thickness. The thinner the wood the more likely to split. Also, don’t try to nail or screw too close to the end of the rung. Allow some overhang. Screws can split the wood too, not just nails.
Don’t over tighten, especially with screws. Once it is in, stop.