Hi B., once you pick the school she is going to go to.....stop by a few times so you both can spend a little time there and check it out so she can see what will be going on there. It works two-fold, helps you be comfortable with your decision in the school and helps her see what she will be doing and all the fun stuff there is at school.
Make sure you always make it a "fun" topic of conversation, beginning now. When she is at home coloring say, "Wow Julia, that picture is great, I can't wait to see all the great pictures you get to draw and color at school ~ how many crayons do you think they have there?".
Clear a spot on the refrigerator, back of the front door, her closet, wherever, and proudly tell her "this is where mommy will be hanging your pictures from school - I can hardly wait".
When reading her favorite book, remind her "I bet you can take this book to school to share one day and your teach can read to your entire class, that will be so much fun."
By doing this, I think you are preparing BOTH of you. I am so blessed that my daughter has been a the same daycare/preschool since she was 3 months old (now 3 1/2 years)...so when we transition classes, it isn't any real big deal for her, more for me and that she is growing way too fast.
When you drop her off, kiss your hand and put it in her pocket...tell her it is there if she needs it during the day...then ask her to give you a kiss to put in your pocket so you have it if you need it. :) (I do this and sometimes give her loving little 'spanks' to her bottom and tell her, "just in case you need a spanking and I'm not around" (mind you she has received 2 spankings in her 3 1/2 years.....)...this cracks her up!
OMG, Emma P said it best....there is nothing, and I mean nothing better, like the sheer excitement and love you get when you pick her up and she comes running across the playground screaming your name!
When you get in the car, rember to ask her what the best part of her day was. I also ask my daughter, "did you get super smart today?" she says "nope"...I tell her "well, then, you are coming back tomorrow until you get super smart". She outsmarted me one day and said "Yes mommie, I got super smart!"...I told her "wow, that is great! then tomorrow you can come back and get even smarter!"
And lastly (sorry for being so long....), when you do leave her, try not to worry if she is the least bit upset ~ the teacher will take care of her and you can bet that she will probably be fine before you can even get your car out of the parking lot. Just keep a positive attitude, don't let her know you are sad too........wait til you get in the car to cry.....and it's okay to!
Hang in there Mommy, you will both do great!