In most cases, this transition is harder on us than them. I remember holding back the tears when my first born went to daycare for the first time. I was so proud of him as he waved me off from the window - with a big grin on his face, and I drove off, sniffling into my Kleenex.
It's not this easy for lots of parents, especially if your child is quite young when they first start, they probably won't be quite so happy to see you off.
Gradual Entry. I'm a huge advocate for gradual entry. slowly start to build up your time there, with you initially, so 2 hrs, then 3 hrs, then 4 hrs and so on. As your child can't tell the time, what they can tell is the sequence of events - eventually they will associate a certain time of day (such as circle time) with you arriving to pick them up.
Routine. Ask for a copy of the daycare routine and work on this prior to your child going. This way snack times, and nap times will be lined up, making it easier on them and their body clock.
Relax. Smile, even if you feel like bursting into tears - children take their reactions from us, if you are acting nervous about the drop off, your child will pick up on this and feel anxious as though something is wrong.
Sleep will regress. Expect that initially sleeping in a new environment, will result in some over-tiredness, as they won't sleep brilliantly to begin with. Long term and once settled in, they will be a better napper at daycare than at home. It's very common to have a great 3 hr nap at daycare and a 45 minute cat nap at home on the weekend, after you have also spend 45 minutes working on them going to sleep.
Crying. Don't be surprised to see tears when you drop them off and when you PICK THEM UP. For nursing mums, they will likely want to nurse straight away as soon as they see you- go for it!
Most children after a few weeks (sometimes up to 6) will stop being as upset on the drop off and pick up, they may infact even look forward to it.
One thing is for sure, your child will get sick when they first join a daycare and this is very hard to avoid. Expect it, and if you have extra time in advance of going back to work, see if you can start the gradual entry a month earlier so that you can get an idea of what is to come before you go back to work, as its a stressful time for a lot of parents.