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Read The Joy of Living
Read The Joy of Living: Unlocking the Secret and Science of Happiness by Yongey Mingyur Rinpoche. It will answer all your questions about meditation, how and why it works, what method is the best for you, etc. You can buy it here.
It's a great method for loving yourself and for understanding that all people, just like you, want to be happy and want to escape the pain. So it will make you more open to others. If you have hard feelings to someone or even hate them, it will definitely help you.
Here you can read a good and easy description of this method.
If you want someone professional to teach you this method, just find some meditation teachers or groups in your area.
If you have too many thoughts in your head or even obsessive thoughts, observe them without any evaluations. They can amazingly help you with your meditation. And in some time you will realise that your thoughts come and go and they are not as huge as you thought.
You can use this method on the go if you don't have time for a formal meditation.
Each method of meditation is good for making it easier for you if you have mental problems, and they can even help you with your practice.
Use your obsessive thoughts or hard emotions as objects of meditation. Just watch them without any evaluation and in some time you will understand that your thoughts and emotions are not that powerful and you can control them.
Concentrate on your negative emotion while meditating and soon you will understand that you can't concentrate on it for too long and it often happens that you start thinking about your laundry or something like this. This way you will understand that all your feelings and emotions are not that powerful and you can control them if you watch them. You can use this method on the go if you are too busy for formal meditation.