When you open your game for the first time each day your lives will be full.. ie: you will have 5 lives and cannot accept more.
Even though your lives are full you will get the popup with your requests from your friends, see image below.
There will normally be 9 single lives and the last request will be several names but just one life, as you can only save 10 lives maximum in your message box.
DO NOT click accept on any of these extra lives if your lives are full or they will be lost forever!
Click on the BIG X top right of the popup to close the messages without claiming any lives.
When you have used your 5 lives look at the top right of the game and you will see a pink envelope.
See image below.
Click on the envelope and your saved lives will be waiting.
ONLY accept FIVE from the message box then close it again to save the rest 'till needed.
If you refresh the game or close it for any reason all the lives stored in the envelope will be lost, but if you have plenty of friends there should be more fresh ones sent.