The first step to take is removing negative thoughts from your life. Take control of your life and remove all such negativity as soon as possible.
It does not matter how big a list is regarding your bad attitude. The thing that matters is you have started working on them to eliminate all of them.
It is not just about forgiving yourself, it is also about forgiving other people who matter for you. Always remember that forgiveness reduces stress and brings joy.
If, by mistake, you are connected with some negative people who do nothing but share negative thoughts, it is better not to stay connected with them.
Want to change some bad attitudes? Here is an idea: why not start helping others who need your support? You will feel more positive after helping others.