Well, many Union and Confederate commanders were taught how to fight with conventional tactics and that's what they used and all they knew how to use. I couldn't see many commanders on either side suddenly switch to guerrilla warfare, since they were not trained how to do so and their soldiers were not trained how to either. However, you still had the guerrilla warfare taking place all throughout the border states and many cavalry commanders, especially Confederate cavalry commanders, like Mosby, Forrest, Morgan etc. employing guerrilla warfare and unconventional raiding tactics to good use.
As for the tactics used throughout WW1, I like to think of the situation in WW1 as a stalemate rather than suggesting that the tactics used were idiotic. The generals, just like in any war, were pressured to take the ground that they were assigned to take and frontal assaults against fortified positions were the only way to do it. You had revolutionary weapons, machine guns, accurate and faster loading artillery, bolt action rifles etc. and all that is dug into highly fortified positions. It was a giant stalemate, the commanders needed to take ground, but couldn't because the defenses were too strong and their divisions were cut to pieces on every attack. There was no other option for those generals if you think about it. The only option they had was to send more men into the meat grinder and try to take as much ground as they could. I think many Civil War generals were in the same situation. They knew no other tactics at the time and they used what they had. They were pressured to take ground, but the only way they could do it is to attack with risky consequences.