I often get this question from people who come for therapy. My answer is that in order to get a grip of your low self-esteem you need to track how your low self-esteem is expressed. In other words, take you calender and write down your behaviors during a week. Write down, what you do and with whom. Also, write down your feelings connected to the different behaviors (1-5 in how stong the feeling is). After the week has passed you can see what kind of situations trigger you to feel bad about yourself. Also start observing that the behavior you want to do when you have a negative feeling, usually is a behavior that will give you some kind of relief in the short run, but more of the negative feeling in the long run. In other words you need to start planning what kind of behaviors you can start training on next time you are in a difficult situation. That behavior will probably make you feel bad in the short run, but it will make you feel better in the long run.
Also, remember that if you run over your needs, you signal to your psyche that you have low thoughts about yourself and then your psyche gives you back portions of negative feelings. If you do caring things to yourself, you signal that you have nice thoughts about yourself and then your psyche, in the long run will give you more positive feelings.
It´s not enough to force yourself to ”think” that you are good if you at the same time show with your behaviors that you don´t respect yourself.
Good Luck!