The 26-year-old actress only wears clothes she feels confident in when she has a big event to go to because she finds posing for the cameras nerve-wracking.
She said: "Being on the red carpet tends to be stressful because there are a million cameras and some are looking for that embarrassing photo.
"So my advice is always feel comfortable in what you're wearing - and that includes your clothes, your shoes, your make-up. That is what will make you feel the most confident.
"Of course, I don't mean comfortable like sweats and Uggs."
Blake likes getting ready for special occasions where she has the opportunity to wear glamorous, floor-length gowns and prefers having her hair down in loose waves.
The former 'Gossip Girl' favourite added: "Honestly, though, I enjoy getting ready for big events - it's like grown-up dress-up.
"Often you see people on the red carpet with tight up-dos, but that makes me feel stiff. For me, effortless hair is much more romantic and lived in."