yes, planks planks planks!!
i've experimented with abdominal activation work (planks!!) first and it works great! the idea isn't to fatigue them, just to activate them, so they work properly during my training to keep my back safe. glute activation (e.g., sky humps) also seems to help a lot.
i particularly notice it helping in overhead pressing (which sometimes puts pressure on my lumbar spine when my glutes and abs aren't kicking in) and in helping me remain upright for my front squats. actually, i find it helps me use my lats properly with chins, too... and hold a good position with push-ups... and rows... not sure that there is anything it doesn't help.
my abs feel more tired after my training, too, since they have actually been working properly.