If you are in a relationship, look for clingy-ness or being needy.
Though, the symptoms of low self-esteem are pretty similar to women. He might put himself down, he might not make eye contact, maybe stares at the ground when walking, etc.
Telling yourself each day that your awesome, and you like yourself, and writing down all the good things you did that day? Since nobody else is going to tell you in life?
I think it’s good to do that,but I think there’s more to it than JUST that. For example,you eventually have to start believing in yourself,realizing that you’re just as good as anyone else.
Learn how to stop paying attention to what someone else thinks of you,and loving yourself for who you are,and accepting your flaws.