Pick your tomatoes at "breaker" stage, when they've just started turning color. Hard green tomatoes will not ripen to satisfaction indoors, but tomatoes that are beginning to soften and blush red (or yellow, or purple, or whatever the ripe color will be) will do just fine.
|Breaker stage tomatoes: photo by Bob Nixon. They can be greener than this!|
We've been saying this since 2011! Read Bob's post about tasting kitchen-ripened tomatoes. This is the best advice I've had about tomatoes ever. It doesn't always work, and you will still lose a few of your precious fruits to really greedy visitors or rots that set in early, but your yields will be far higher and your frustration levels much lower.