Mm, my biggest one is to not wear clothing or accessories with obviously huge logos. If I do have a designer item with a big logo, I turn it around so you can't see it. I try to find items with the smallest or subtlest brand logos visible.
I don't want to be a walking billboard for the designer when I'm the one paying. And it's a bit ostentatious, like I'm screaming, LOOK LOOK, IT'S A LOUIS!!! I like my clothing to whisper, not shout.
I also don't like to buy the signature items from brands because it's recognizable when it's off season. Too trendy items loses its trend-factor too fast and you get sick of it.