I was wondering if it's best to duplicate the same posts in Twitter & Facebook or should each social account be used in different ways? And if so, what would be some good tips?
It is not a big deal to post the same thing on Facebook and Twitter. I do it myself, besides there are autopost/scheduled posting tools that you can use. And before Twitter has an option to post tweets on Facebook. Same goes to instagram that allows you to share your post also on social media sites like Facebook, twitter and tumblr, right? So, there is no biggie on it.
I recommend posting the same content across all platforms perhaps just tweeking some text for length and also if you are tagging any other business or account. Every once in a while posting just to one platform might have a purpose too, but for the majority of posts blast them out across all networks.
It's okay, you can use the same content across your social sites. If you're uncomfortable that way, you can change up the wording. Like what others suggest, it's not such a big deal if you blast it.
twitter has a limit on characters so you might not even be able to do that, plus the audience might be different...if it's just a link and short text then sure...or even a photo and some hashtags
There is no problem when you write a content on your blog and share it on social media. Or when you write something on Facebook and later copy it to another site but you must remember that people who like your profile on FB probably like other sites and they can be bored sometimes.
You don't have to worry about duplicated content if you promote something on different platforms. Take Facebook as an example. It doesn't even allow crawler to visit its subpages.
It's okay if you duplicate your posts, nothing's wrong especially when you are promoting something then you really have to post it again to another social media sites.