Yes - I have tried this unfortunately with not very much success. DH's family were always quite against me from the moment that we met but I was always pleasant and caring towards them. I babysat his nephews and nieces and even hung out the washing when we went to his sister's for dinner (I had to sit on the floor in the kitchen to eat 'cos there was no space at the dining table!).
It carried on when we were married and his parents came to live with us. His mother was particularly nasty (although she was in a wheelchair) and would call me names ("whore" being a favourite) and on one occasion chased me around with a wooden spoon. I ignored it because she meant the world to my DH.
When she was admitted to hospital with breathing problems, I took turns staying overnight with her and was actually mistaken for her daughter by hospital staff. Her own daughters were too busy and wouldn't even help her go to toilet. Caring for her was full-on and I was never sorry to do it. I bathed her, dried and brushed her hair till it shone, rubbed her arthritic arms and legs with oil.
She was an extremely difficult person and eventually her hate overcame her and she began to turn on my DH. They had a terrible row which resulted in her going to the police and accusing us both of neglect. Luckily for both of us, social services were aware of her history but sadly for my DH, she moved out four years ago. He saw her a couple of times after that but she passed away just before Christmas.
I'm not telling you guys any of this because I'm a martyr or a saint - far from it - I actually have very little patience! But I treated her better than I've treated my own parents and with more love and care even though I knew that she hated me. I'm not sure I would ever do that now I have a DD but still, now she's gone, at least I have no regrets. The rift between her and DH was in no way down to me and whatever she said about me, the opposite was true.
At the risk of sounding preachy ( although this is a religious thread ) someone once told me that when it came to your enemies, you should "kill them with love". I think that's a great adage and I'll never be sorry I followed it.