My windows have horizontal mini blinds as well as curtains
with valence boxes. The windows have two layer of glass.

On a cold night, what's a good way to reduce heat loss through
the windows? Do the blinds make much difference?

In summer it can pay to reflect sunlight hitting east and west
windows. Vinyl blinds let some light through and probably
absorb some. Is there a better way to reduce solar heating
through windows?