When you toddler goes from a crib to a "big kid bed" it's a big deal. Let your child have a little say in the bed she'll be sleeping in and you might find the transition from crib to toddler bed is a whole lot easier.
A crib has sides and this gives many children security. Moving to a toddler bed with small rails to keep them from failing out, still works well but it may not offer the mental security that a crib did. Letting your child look at different beds and choose the one that she'd like to have her nighty-night in and you will find that the step from crib to toddler bed will be pretty seamless for most kids.
If your little guy likes firetrucks, why not go for a toddler bed shaped like a fire truck? If you have a little princess that loves all things pink, let her rest her pretty head in a bed fit just for a pink princess. There are also beds shaped like boats and for the child that likes it plain and simple, well he can have that too.
Another great idea is to establish a bedtime routine. Boundaries and routines make children feel secure and a nightly ritual of a bedtime at a specific time, along with getting ready for bed that can include a bath or shower or just washing up and brushing teeth, putting on pajamas and maybe a bedtime story or a quiet talk time and doing that every night will let your child settle into a relaxation mode for bedtime quickly.