“I hope you are back on your feet soon,” “Everyone here is thinking about you” and “I wish the very best health to you” are general get well quotes that can be used in most situations. “Get well cards have become so entertaining that if you don't get sick you're missing half the fun” is a humorous way to cheer up a sick friend.
If the purpose of a get well card is to comfort a family member or a friend, the message can read something like “We all wish you a speedy recovery. Don’t worry you will feel better soon!” to communicate warmth and reassurance from the loved ones. “We miss you so much” or “We are eagerly awaiting your return” are also appropriate in most situations. If the sick person is religious, a quote can mention prayers, spirituality or the supernatural: "We pray that God will watch over you, heal you, comfort you and give you peace at this time."
More humorous types of messages include “Get better soon or I’ll break your legs again!” or “Hoping for your complete recovery because I don’t want to come to the hospital for a second time!”. "If your immune system was a lawyer, I would fire it. It doesn't seem to be defending you well enough" is also a message that's sure to put a smile on the face of a sick friend.