Let the soil completely dry out before watering and then give them soil a good soak.
String of Hearts only need infrequent diluted fertilizers. At most once a month is more than sufficient.
Like most indoor plants, String of Hearts cannot tolerate direct light, but must be kept in plentiful indirect light. Keep them near the brightest possible window.
Keep your String of Hearts between 18 and 26 degrees and away from direct air conditioning drafts.
You can repot your String of Hearts once a year.