Well. There are two answers to this.
Perhaps it is messy and unconsidered, but if you’re reading this it probably isn’t so much the lack of concern for its appearance.
I would suggest that your major issue is that you have bought pieces and decorated along the way without a great deal of thought for the end game. This is very normal and typical of family houses.
To tighten it up do a major Marie Kondo edit (Google her, she’s a tidying magician, then read her audio or print book The Lifechanging Magic of Tidying). She will teach you how to keep possessions you love and that is the essence of a happy home.
When you’re all done with this you will have MANY fewer possessions and you will have been able to look long and hard at the things of beauty in the home and may want to give them new-found prominence. It’s not been fashionable for a while to keep collections on display but this is changing and if you have an ordered collection of little Michelin men or Toby Jugs or Lego give it proper prominence, give it some elegant shelving and a light it well, paint the shelving dark, or bright, or a colour that best shows off your collection and show it with pride.
The unconsidered bit: here’s the thing.. did you go down an industrial route, then a shabby chic one, then a French country vibe.. so hard isn’t it?
Try to keep it tight by deciding what you stand for and where you’re headed with it. If you are going down one of these, or any route, do it, and do it wholeheartedly. An exposed cable leading from your wall or pendant lighting does not a funky vibe make!
If you imagine your possessions as wardrobe, if you wear your diamond necklace with your beach shorts and a low-cut backless top you will just look weird. Just because they all looked good on separate days in separate shops does not mean they will look good when worn together. Sometimes you can love something but need to leave it in the shop for another project, another day, another owner.
And that for me is where Pinterest comes in. Make yourself a relevant board and post a photograph of the glorious item to it so you can plan the next project or house, or dream.