Maya, I've recently used a mantra of "color, texture, pattern, shine" in my outfit-building. I'll look over my outfit and make sure I have:
1. a pop of color,
2. some sort of texture (and it can be anywhere from smooth like silk or cotton or more pronounced like cables in a knit or a pebbly texture to a coat),
3. a pattern (I have way too many solids and feel flat at times too),
4. and a bit of shine! Sometimes this is as easy as wearing patent shoes or maybe a metal bracelet or earrings. Sometimes I feel silk shirts can have a good sheen to them, and this will count for me.
I personally like it best when each outfit has some interest in each of those categories. I have a lot of smooth cotton-y knits as well, so when I don't have varied texture in my outfit I will trick the eye by using pattern instead to add interest to my wardrobe.
To incorporate actual textures, try using thicker knits, perhaps in a scarf if you don't want cables in a sweater. You can also get smooth-textured pants in a pattern, like checks, pinstripes, or a subtle plaid. The different qualities in a fabric (soft and flowy and draped or stiff and structured) can have an impact on how an outfit looks too.
Simplified, I think it comes down to contrast. Since I wear a lot of solid colors I am trying to incorporate patterns and more pronounced shine and textures to balance that. Hopefully this makes sense?
