In addition to sending lives to friends, you can ask for them as well. To request lives, tap on the bar with the heart icon in the top right corner of the screen. A menu will appear with two buttons: Ask and Send.
Tap Ask to send a request to friends. A window will pop up with a list of friends who you may request lives from. Select as few or as many friends as you want and press Ask. A Facebook window will then appear. Press the Send button.
You can claim lives that friends have sent you on the News tab. When friends send you lives, a heart icon appears on the News tab. When you open this tab, you will see the friends who have sent you lives. Tap Claim to add as many lives as you need to reach the maximum. Any remaining lives will remain in the News tab during 2 weeks. You can claim them whenever you need them during this period.