K.B.
This is what I do with my daughter (3 years old) who goes to preschool two times a week, she does not have separation anxiety but does need a routine.
*** Walk in hang up book bag and coat if we have those items (if possible do this anyway even if item is not needed, it just creates a routine that way they know what is coming)
*** Ask if the child needs to use the bathroom before you leave, or have the child use the toilet to help establish routine again.
*** Then I tell her that I will be back when the big hand is here and the little hand is here (maybe even draw it on a piece of paper put it in a pocket so they can take it out and look at it whenever needed) if it is a digital clock in the class room then write down the numbers.
*** Say hello to the teacher/helpers which might help transition mind into preschool mode. If there is free time when they arrive, or get there early, ask child what they are going to play with.
*** Say good bye, hugs, kisses, tell them again that you will be back shortly and to listen to the teacher and have fun... and leave, do not watch or hang out that sends a vibe that you are worried/anxious which the child picks up on and mirrors back making the issue worse.
These are some of the tips that our preschool teacher game us, it should only take 5 minutes to drop off a child, dragging it out can create more anxiety. Most preschool teachers will give/have tips on separation anxiety, so ask for tips.