I was spanked as a child. My parents were spanked as children. So when I had my son, I thought that was the way it is. I have never spanked my son, but I have smaked his hands, or butt a time or two. But I learned that this is not effective! And it made me feel terrible! He started smacking me back, smaking other kids, smacking the cat, etc. I knew right then and there that smacking him is wrong and now I don't ever do it any more. I found it much more effective to give him time-outs, or keep him from watching his favorite show on TV, or take a toy away. For instance, I tell him to pick up his toys, I get "no" and so I pick up one of his toys, and carry it over to the garbage can and ask him "do you want me to throw them away?" He starts throwing a fit "no, no no no!" and crying. I say, if you don't want me to throw them away, you had better put them away. You wouldn't believe how fast he puts them away. On the occasion he still refuses, I do throw it in the garbage, then later when he is in bed, I pull it out, and put it downstairs in a closit for a couple of months. Toys are too expensive to just throw away! But this seems to work well.
For bath time, I use the favorite show tactic. "Do you want to watch Wild Kratts?"
"Yeah!"
"well them you better take a bath, then we can watch your show..." If he still refuses, I put him to bed early without show.
I think you just have to do what works best with your own kid. Kids require a LOT of patience though. It can be really tough.