Making tea the way he likes it, no sugar.
(Except when it's necessary to drug him using the sugar.)
Not performing experiments on him without his permission.
Or with it, really.
Not playing violin between 12pm and 6am.
Or playing really softly.
Keeping experiments on their designated shelf in the fridge.
Not contaminating food with experiments.
Not forgetting to tell John if there may have been some slight contamination.
Playing John's favourite violin song after he wakes up from a nightmare.
Interrupting dates that are bound to go horribly, dreadfully, wrong.
Rescuing him from drunk dinners with Harry where she moaned about Clara to no end.
Not insult his other friends.
(Read- by telling the truth. Don't do it.)
Telling him interesting facts about bees, which John seems to be fascinated with.
Knowing everything medically relevant about John.
(Oh, he doesn't? What could he possibly be missing? A bee allergy? No, that's preposterous.)
Informing him before you go chasing after a criminal, so he can grab his gun. Or back out.
Helping him hide the evidence when he kills someone, even if it's a criminal.
AN- I'll probably continue this as new things occur to me, but don't expect any regular updates.