3 steps to add a Polaroid effect in Photoshop.
You can see what channel you are viewing along the top of the window. You'll want to create a line that looks like a checkmark with a flat left side for the RGB channel. Click in the centre point of the line provided and drag the leftmost corner upward — this brings the black point up and "fades" the darkest image parts while leaving the highlighted areas intact.
Then, make a slight S-curve for each of the individual colour channels. Click in the centre point of the line provided and drag upward or downward on the curves. This action will dull the colours in some areas and intensify them in others to mimic the look of film.