Warmth is the most important. Putting them in the dark doesn't help, but I'm not sure that it does any harm. I'd leave them on the window-sill, and I'd leave some sort of ripe fruit with them.

Last year I had a big bowl of green and orange tomatoes on the kitchen worksurface. Red ones never appeared, but the level of tomatoes in the bowl went down. I realised my son was snaffling the ripe ones the instant they became ripe ;-)