Valentine’s Day presents an opportunity to experiment with candlelight, a really old-fashioned light source. Candles provide a single, pure pinpoint of fire that is both warm and intimate at the same time. You know you’re a real photo geek when a romantic candlelight dinner inspires you to break out the camera and tripod!
Candles are actually one of the harder types of fire photography, because they don't give out very much light on their own. The solution, of course, is to use more candles! Shooting candles will require careful exposure management, as the contrast between the bright flame of the candle and its surrounds can be high.
In terms of your camera settings, if the candle flame is still and there is no other movement in the shot, you can use longer shutter speeds and a tripod to get the moment. If there are people in the scene, you can't lower the shutter speed too much as they will come out blurry, so compensate with a higher ISO to avoid motion blur, and open up the aperture as wide as it will go to let all that light in.
The light from a candle is a beautiful warm glow, perfect for illuminating people, so consider using candlelight as a natural light source for portrait photography.