I am at this stage with DD2(2.3) (I also have a DD1(4) and DS(12))
First and foremost,IME Don't rush into this,it's difficult to go backwards,and if she isn't climbing out of her cot,then wait a while.
I think all too often we feel "pressurized" by peers etc. to make this change,when all too often,its us that wants to start this new step,and our DC's often aren't ready.
If you do proceed,I would start with her nap during the day in the "Big Girl's Bed". I would have prepared her for it,by shopping together and choosing her bedding together,and having lots of conversations with her about it.
If she has her Daytime Naps in it only,you'll be getting her used to it slowly,and be able to see how she will behave in it.It'll also give her time to "get over the novelty" of it all,and let the "excitement" die down before trying a night in there.
You can try explaining that she needs to stay in her bed all night and only get out for the toilet,or when Mummy comes to wake her up.
(I've just bought a Disney princess clock,which is a "bedtime trainer",has a "night" face,and a "day" one)
If she does keep getting out etc. you can try all the usual tips such as Rapid return,Star Charts or a stairgate on her door.Good Luck!