It's really worth it - it's probably about £2 on amazon with postage.
I can't remember much of it as I read it yonks ago and only have one DC so haven't been able to put any of it into practice but I have a sister and remember reading all of it and nodding along enthusiastically!
I have read that book and also How to Talk... many times and they are both terrific and do help (not that you would know from my performance lately.. Must read them again!).
But here are some highlights to add on what others have said:
- don't solve every quarrel. "I see two boys with a big box of blocks but both of them need triangles At the same time. That's tricky, but I am sure you can figure out a way share them" (then leave the room)
- don't put your kids in roles. "Oh Johnny, why can't you be more tidy like your sister?"
- do tell them you love them individually, not "all the same". "What would I do without my Daisy, who draws fantastic rainbows and always helps me push the trolley at the shop?"
- don't go overboard in telling off the aggressor. Instead, tend to the sibling who has been bashed/insulted etc. " oh no Johnny, that looks like it really hurts. Let me get some ice. Your brother needs to remember to use his words not his fists when he gets angry." (ie the aggressor won't be rewarded with attention even if its negative attention)
That's all I can remember but those are some of the best tips. Clearly I have read this book many times!