Many teenagers spend several hours a day on social media. Supporters say that it helps young people to stay in touch with friends, share their interests and learn about the world. Some students even use it to find study groups or to follow teachers who post useful lessons. Critics, however, point out some problems. Spending too much time on a screen can reduce sleep, and seeing only the best moments of other people's lives may make a teenager feel unhappy about his or her own. Also, personal information shared online may be seen by strangers. Experts therefore suggest balance rather than a total ban. Families can agree on limits, such as no phones at meals, and teenagers can think carefully before they post anything. With these habits, social media can be a useful tool.

Question: In the last sentence, what do 'these habits' refer to?