What is the occasion for? Just every day wear? Workwear? Going out wear? Meeting friends wear?
It's difficult to really say much just on a picture without context.
Here are my totally honest views:
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Never wear that cardigan with that combination again! It might look good with some dark skinny/straight leg jeans, ankle boots, and some sort of plain top, like one of THESE, in whatever colour suits you.
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Since you are wearing a dark top, you need to wear a dark bra underneath. It might just be the camera, but it looks like you have a day glo white bra beneath the purple top. Not a good look.
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I hate coloured/patterned tights with a passion, so I am biased on this point I will admit. But colourful tights being matched to tops, handbags, hairbands, whatever...I have always hated it. It looks tacky (imo). But again, maybe that's just a question of personal taste.
*Skirt length....you can probably get away with actually. But not with knee high boots. I think this is it actually - everything you are wearing works, but not together.
SKIRT
The skirt would work much better with opaque black tights (or dark navy, I can't tell what colour the skirt is), and ballet flats like THESE or THESE, combined with a plain top in a neutral colour such as THIS or light grey, or whatever neutral colour suits you.
CARDIGAN
I've already gone through the cardigan above.
PURPLE TOP
Would look better coupled with a black vest top underneath, to prevent it being see through, and a pair of well fitting straight leg or skinny jeans in a dark colour.
TIGHTS
Burn them
BOOTS
There is nothing wrong with your boots, but wearing knee highs with a short skirt is a bit...I don't know. It's just not a good look in my eyes. I am not a big fan of knee high boots at the best of times, so although there is nothing wrong with them at all (they look like nice boots), I can't give you any ideas of how to wear them.