The solution is to have clothes that they want, or even are desperate, to wear! With our toddler this means adding "cool things" to ordinary clothes. At the moment anything with e.g. fire engines or dinosaurs are successful. The giraffe applique was a big fail and will be removed and replaced with something else.
Adding appliques, home made or store bought, also ensures that the clothes are unique and less likely to get lost at nursery.