All fantastic answers. Voting for this one was tricky. Knowing the centre in advance helps so much. Sell the positive benefits of being in daycare. No different to when your child starts kindergarten. The earlier your child is in pre-school, the easier it is to orient them to primary school level.
Get to know the staff and the centre well before your child starts ask if you can make a few little visits before their first day. Talk to your child about the staff's names, how nice they are and all the fun things they can do there. Remind them often that you will always be back to pick them up soon.
The daycare my daughter went to recommended taking your child along to the centre to have a play and get used to the place with you staying there with them once or twice before they started there. We did and I think it helped. My daughter got used to the place and I got to see her happy there and was reassured that she would have a good time and that their facilities were top notch and staff well trained.
She didn't cry at all the first time I left her there, but the second time she knew what was coming so she did cry a bit. I pretended to leave but watched her through a window for a few minutes and was immensely relieved to see that she stopped crying as soon as I was out of sight. Don't dawdle. Hanging around too long just upsets them more.
Make sure they know you'll be back to get them and when and be there on time. It can help to let them pick out their own gear (backpack, lunchbox etc.) to take with them.
One thing that I did before my son started his daycare was to organise a play date with another boy who was starting at the daycare centre at the same time. The boys got along very well, so when it came to their first big day, they were excited because they knew they would have a whole day to play together.
Most kids adapt easily and the teachers are trained to make their first day less scary. I think often times it's the parents that suffer more. If you are dreading your child's first day at daycare, why not organise a fun day for you - catch up for coffee with a friend or enjoy a nice shopping trip.