Edit your Wardrobe: Before you go shopping, weed through your wardrobe to find out what works and what doesn't. Keep the items you want hung up. The remaining items will fall into the "Donate to a clothing charity pile" or the "Might work if I get them altered pile".
Create a few Looks: Do this alone; with an honest, stylish friend; or hire a personal stylist. Try on your best pieces to plan your outfits and to assess what you are missing. Have you noticed any "holes" in your wardrobe? Do you need a some new accessories? Are you missing the always necessary "Little Black Dress"?
Create a Style Inspiration Diary: Get your favorite fashion magazines together. Rip out pages of any looks you may want to try. Place these pages in a three ring binder or secure them to the pages of a notebook.
Make a Wish List: Using your style diary, create a list of items that you need and what you want. Take this with you whenever you are out shopping. This will avoid those impluse splurges and you will shop for the key items.
There is a way out of this "What do I wear dilemma!" A properly stocked closet with all of the right items. How do you plan your wardrobe?