Baby sleep is so much easier and less stressful if you just expect it to be complete nonsense for at least a year, possibly two. In my experience. And just do things that make it manageable rather than trying to expect it to conform to any particular pattern or force it into something somebody wrote in a book. They do sleep eventually, even if you do nothing at all. It is quite magical when it happens.
If this approach appeals to you I can recommend you two nice books. Read the extracts on the authors' websites, and choose the one whose tone you prefer: The No Cry Sleep Solution by Elisabeth Pantley, and The Gentle Sleep Book by Sarah Ockwell Smith.
If you would prefer to be more proactive, I've found some interesting ideas on this website, but I'd caution that it suffers from what I consider the usual baby sleep gubbins - a set of beliefs which seem to surround every site, book, or other source of sleep info, all of this I find unhelpful/problematic and I would caution you to take it with a pinch of salt.
- The idea that certain sleep milestones (e.g. night weaning) "should" or even "must" happen by a certain time. (Implying: If they have not, you should be making them happen by any means necessary and/or you're a bad parent if you don't.)
- The idea that just because a baby/child has done something once (e.g. sleep a certain amount of hours, go the whole night without feeding, go to sleep without X prop) that means they can do it in any circumstance at any time and the fact they are not means they are manipulating you. (In reality... doing something once doesn't mean you're ready to do that same thing regularly or easily. Babies aren't different to that.)
- The idea that sleep training is something you HAVE to do sooner or later, just like potty training. (Not true. You can actually just wait it out, if you want to.)
- The idea that sleeping independently is the holy grail and/or that helping your child to sleep in any way is bad and wrong, the cause of all sleep problems ever, or any other pointless judgement/exaggeration. (Obviously it's easier if a baby/toddler doesn't need your input to sleep, but it's not bad for them if you are happy to do this.)
For example - the "baby sleep homework" on the 3-6 month page linked - point 1 is OK. Point 2 is unnecessarily doom laden and scaremongering, and also utter nonsense. All babies grow out of needing to be held, rocked, fed (or whatever) to sleep. Some sooner than others, granted. But if nothing else - at some point they get enough language to reason and negotiate with. So of course it won't go on for ever and ever just because you allowed it at three months old.
I find the info on the site useful, and the idea that 3-6 months is a sort of "window" where changing sleep patterns is easier than it is likely to be if attempted later is a useful one, but all of the unnecessarily judgy language puts me off massively.