What one trick can you do with your curtains to let more light into your living spaces? Try framing your windows with them instead of just providing some shade. Place them in slightly longer curtain rods than your windows so you can draw them further and maximize light streaming from your window.
You can also opt to buy discount shades that's almost sheer so that light can still seep in even when they're drawn.
One other you can do is to install sliding windows on walls (made from the same material or not) separating certain rooms, which you can open during the day.