The short version: by using a comfort object.
Oh, you wanted more detail than that? Fine.
So, at 9 months I was worried that Will wasn't sleeping enough. I wasn't so much concerned by the not sleeping through the night (I really think kids will sleep through the night whey they are ready.) But in addition to not sleeping through the night, he was going to bed late (around 10 most nights) and getting up early (between 6:30 and 7) and only napping for 45 minutes twice during the day. I discussed with his pediatrician and she agreed, not enough sleep. We discussed the various theories on sleep and agreed that it depends on temperament of both parent and child. (Most helpful discussion ever right?)
In the end what she recommended doing was getting him a comfort object. We settled on a teddy bear and started giving it to him every time he nursed or we put him to bed. I also co-slept with him and the bear for a week or so. Then we moved, and started putting him to bed at 7. He cried some for the first few days (10 minutes or so) but it got better after that. For awhile I worried that he was going to cry every night when we put him down because he got so used to The Routine that he would start to cry as soon as he was done nursing. But he got over that, and now he goes to bed without a fuss most nights.
It is true that sleep begets sleep. Going to bed earlier led to sleeping through the night (after a few days) AND better naps. He has been waking once in the night recently, but I blame the FOUR teeth that erupted in the last 2 weeks.
So there you have it. Questions?