Hi Beatrice.
I doubt I can be of any help because my LG never once cried when I left her at school (she started jan this year at 20 months). well, she 1st went to a creche at my work and she would cry when I left her there but I also had a weird feeling about that creche. It just didn't quite "gel" with me. So maybe she felt the same.Ii took her out before even a month was up and had to pay for an extra "notice month" but i didn't care. At her new creche, she absolutely flourished. She hardly even has time to say good bye to mommy once she sees her teacher and her friends.
I didn't do anything specific to get her used to the idea of going to creche. I could almost feel that she was ready.
I guess the advice that I can offer is to TRUST YOUR INSTINCTS! the 1st creche she went to was more expensive than the one she is in now, top-class facilities,security & location

but that didn't necessarily make it the best option for us. Good Luck