A way of mixing and matching would be to organize your wardrobe according to colors, patterns and styles. This way you will have all your sports outfits in one place and all your elegant outfits somewhere else. Once you do this you can start figuring out what type of outfits you can create by using your own clothes. This way you can easily have vintage outfits with some elegant accessories or even romantic outfits with modern vintage and retro accents.
There are many celebrities out there that are very fond of this type of fashion for instance Alexa Chung, Dita von Teese or the famous Gwen Stefani. Mixing various fashion styles will give you a wonderful and personal look that will surely be a nice change from the everyday routine. What you should be aware of is that this mix and match style is not equal with the grunge style of the 90's. So, in this respect you should choose carefully between the patterns and styles.
Using some old accessories will help you create outfits using the clothes you already have. If you are planning to do some shopping then you should definitely choose some interesting clothing items that you will be able to mix and match with the things you already have.
This type of fashion can be a great way of reinvigorating your wardrobe without investing serious amounts of money into buying some new things.