There's no reason to feel hatred towards any person for being flawed. This applies to yourself when you eat too many donuts as much as it applies to a serial killer that tortures people. It simply doesn't make sense to feel loathing for anyone. Pity is the rational response towards the flaws of humans.
This doesn't mean people can't be improved to a large extent with an improved environment. This definitely works, which is why some self-help books work for some people or why joining the military can help some people improve themselves.
This realization also focuses your efforts on the environment (food, sleep, exercise, books, etc) which is another great aspect of it. Knowing that the way to improve a person is through environment removes the shame of failure. The answer is always to improve the environment and never to blame the person for not being better than they are genetically. Blame the environment for not being good enough to help the person, and then improve the environment until it is.
Something like that, it's part of Louise Hay's How To Love Yourself, a one-page list of things. Also I learnt from Effortless Mastery (about piano playing) to stop all the negative self-talk! Which I used to do a lot. Saying awful, cruel, mean, self-defeating things to myself that I'd never say to someone else. Being kind and patient with myself. I guess I had to learn that while it's great trying to being kind to everyone--you yourself are one of those people. That also helped overcome the very low self-esteem I'd been bullied into at school and at home. And helped with happiness in life. :-D
The first one isn't actually an advice but a friend once told me this: "We start dying when we stop being a child."
There are many things behind that advice. When we're kids we're always curious, we ask questions, we seek answers, we don't care about making mistakes, we're spontaneous, etc. I could list dozens of things. At some point in life, we stop doing those things. We stop being a kid. We stop having all those dreams we once had. That's when we begin to slowly die. In this world of grow ups fighting each other because of stupid things, I'm always trying to remind me myself to never stop being a child.
The second one is related to the Nonviolent Communication approach by Marshall Rosenberg. There's always a big difference between what someone tells us and what we understand. Most of the time we implicitly make a judgment about others' actions and that judgment is just something from our mind. Many times we get offended (or upset) by something we don't realize the other person had no intentions whatsoever to offend or upset us. In the end, it's actually an exercise of empathy: if something is upsetting or offending you, figure out why before engaging in a useless fight with someone else.
Embrace the change, learn new skills, get new experiences. Do not settle.
Don't care too much what others think
Stoicism
Memento Mori
Be strong.
Don’t complain.