
Nunca había oído "de bien en mejor"... yo siempre había oído "cada vez mejor".

I'm puzzled :/
The fact that you've never heard it is something I can't discuss, but when I googled it I bumped into Cervantès's Don Quijote, and a blog. Links below.
If you're sure it is not correct I'll change it to whatever sounds right to you, but please double check this :)
http://dasdelluvia.blogspot.com...-en-mejor.html
http://books.google.fr/books?id...jor%22&f=false

actually it's right :O although I'd never heard it before, and that I still think that my version is more common :P but I've just checked it in the RAE and your version appears...
http://buscon.rae.es/draeI/Srvl...US=3&LEMA=bien
As we say here: nunca te acostarás sin saber una cosa más... :P

I'm sure your version is used 90% of the time, as I've never heard mine when I was in Spain. Feel free to tag it appropriately so that people know it's not really common. :)