You’ve heard me sing the praises before of low winter light levels for photography and how it’s nothing to be afraid of. It’s not. Honestly. It’s not a matter of cranking up the ISO and getting on with it. Sometimes either the contrast is simply lacking (things cal look a bit washed out of flat) or the differences in light levels between the bright bits and the dark bits is too wide (in the past this was the ratios we banged on about). Do you expose for the bright or dark bits?
At the school shoot below I had to light every single shot. Where possible I used bounce flash (using white walls into nice large diffused light sources) but where the walls were coloured (and so bounced light would have picked up wall colour with it) I had to use directional light in place of a where a window might be. Directional light helps with contrast too. If you need help with your lighting, do please get in touch.