How to succesfully base a character off a real person

I've had my bad experiences with basing characters off of real people. Now almost all authors have based characters or events off of real events or people in their life. I myself had based most of my original characters off of people I knew. First I will be giving you a quick list of characters I wrote and who they are based off of
Nancy: Now most main characters I usually base off of myself
Claire: This was actually based off of Keira Knightley. I just got that mental image of Keira as Claire and I stuck by it
Will: I based it off of my ideal prince

When I was writing the City of Gold book I unfortunatly told a friend of mine that the character Lily was based off of her. The problem with that is that it sounds both creepy and usually ends with that person obsessing with the fact they have a character based off of them. My rules for basing a character off a real person is simple:
1. Do not tell the person that a character is based off of them
2. Base it off them loosely and try not to make it obvious
I broke the first law today when I told PM that the character Maggie kinda acts like her several times in the book. Well have a great week and please visit the Ilovegaryclub.blogspot.com. Please.
-AM