Lydia was 22 months old as well when Alex was born.
When my tummy became noticably big (which was fairly early into the pregnancy actually) we mentioned to her that mammy had a baby in her tummy, but we didn't bring it up a lot - it was just to explain why my tummy was getting so big.
Also she used to jump on me a lot so we had to tell her to stop leaping onto my belly and be a bit more careful.
As it got nearer the time - about a month or so before the birth, we started talking regularly about the baby. We had pretty much settled on the name Alex, so we would say that baby Alex was coming soon. We\d tell her about babies and what they do (cry, sleep etc), and we were telling her that he would be very small and not be able to do much at first so we'd have to do lots of things for him and that she'd be able to help like a big girl.
We got her involved when we bought things for him (nappies, clothes etc) and made a fuss of her when she seemed interested.
When I went to the hospital to be induced, she went to stay at my friend Amy's house for 2 nights. She knew that we would be bringing Alex home and Amy got her to draw a picture for me and a picture for Alex to welcome him.
When she met him for the first time we told her how happy Alex was to meet her and how he loved her and that she was now a big sister and that's a very special thing to be. We tried to keep her as involved as possible.
She was quite shy of him when she first met him - she was nervous about touching him and wouldn't give him a hug or a kiss or anything - not that she didn't like him, she did, but she was shy (which I guess is understandable - he was essentially a stranger to her).
After a few days though she gained more confidence around him. We encourage her to give him a hug and a kiss good morning and good night every day, and she tells him she loves him and we tell her that he loves her too. It's true - they absolutely adore each other. You should see Alex's face light up when he sees her, and they are always making each other laugh. Lydia spontaneously gives him hugs and kisses all the time now, and tells him she loves him.
She does have an annoying habit of taking toys off him whilst he's playing with them, when she suddenly decides she wants to play with that specific toy. We're always telling her off for not sharing. But it's only a minor thing - they do get along with each other very well.