For us what makes a big difference is:
-Notice. Don't just change the activity abruptly because it makes sense to you, lead up to it gently. "We're going out to the shop in a few minutes. We'll play for a few more minutes, then put your coat on." "We need to do a nappy change in a minute." Repeat 2 or 3 times before actually putting it into action.
-Involvement. "We're going out now, can you get your shoes/coat?" "It's time for a nappy change, can you get a nappy?" If your DC is too young to understand these things, just say them and then show what you mean (by getting the shoes, encouraging DC to follow you, point at the shoes etc)
-Acknowledgement. "You don't like having your nappy changed, you really hate it!"
-Distraction. "Oh look there is a picture of a cat on the nappy! What does a cat do?" Etc.
For us distraction only works after acknowledgement. If I try to distract my DS without acknowledging his feelings he just wails/struggles even more.
Another thing that is important to remember is that acknowledgement does not equal giving in. I think this is what happens with a lot of people, they think that as soon as they acknowledge the feeling it's a slippery slope to the child and their wishes ruling their life. You acknowledge their feeling so they feel understood, and then you explain what needs to happen. If you can compromise or make it better in some way, then do. E.g. "We'll change your nappy now, and then we're going to have a snack! What will you have, raisins or banana?"
A toddler has very little control in life and a lot of stuff just happens TO them because an adult decides. The above helps them get the feeling of some control while still allowing you to do what needs to be done (and hopefully with less of a struggle). I do think it depends on the temperament of the individual child though, but the above all really makes a big difference with my DS compared to when we don't do that.
There is actually one more that I haven't mentioned here (because I'm guilty of forgetting this a lot with DS):
-Choices. "Do you want to wear your shoes or your wellies when we go outside?" "Do you want the nappy with the dog or the monkey?"