I honestly think it depends on what your child is like. But I dont think every telling your toddler they need to do something because of baby coming soon is ever a good idea. I feel like it puts pressure on the LO and is already setting up expectations that they have to live up to.

Here we talk about sprout every day. they tell sprout they love it and cant wait to meet it. DD2 is still in the cot although its been converted to a toddler bed at the moment. She knows that in the next couple of weeks shes moving up to a big girl bed becuase she will be 2yrs (and also so sprout can have somewhere to sleep).

Communication is big here, and we dont put pressure on them. I dont even ask them if they are going to be good big sisters. We just talk about them being big sisters and being lucky enough to have a little brother or sister.
We do have the theres a baby inside my mummy, and we read that. But Ive owned that since before DD1 was born as I used the book for a uni assignment once.

Go with your DD'spersonality, you will know what will and wont work.