Self Esteem
Self esteem can be defined as a generalized positive-negative attitude toward oneself; that is, how positively or negatively  an individual thinks and feels about themselves.
Low self esteem
An individual with low self esteem have little confidence and/or belief in themselves.  They therefore lack purpose and a sense of self worth.
High self esteem
High self esteem is not self love, but the general appreciation and value of oneself and one's personal worth. Individuals with a high self esteem have a positive attitude and are confident that they have the ability to control their lives and achieve their goals.
This aspect of an individual focuses on external cultural evidence e.g. social status, attractiveness, number of sexual partners  in order to a) determine what to strive for and b) measure accomplishments.  
Higher (inner) Self
However, self esteem is not limited to external cultural achievements (ego). The ego tends of offer a temporary feeling of self worth, sometimes it even fails to accomplish this, which then drives us to pursue some other external goal.   Genuine self esteem is concerned with our mind and emotions and how we interact with the world in which we live.
Interestingly, as we get older, normally by middle age, we start to become more and more aware of our deeper spiritual selves.  Here our goals are less tangible and more subjective than the external objective goals of the ego ... they go deeper and are longer lasting.  With this awareness of self comes the realisation that we, as humans,  are more than what people see when they look at us.
Self esteem (not the ego) is birthed in early childhood and is rooted in our inner self.   The more we acknowledge and value our inner existence, the less we will limit ourselves to just our appearance or  worldly possessions.   As self esteem develops, the more we will celebrate, respect and love ourselves and care for others.
The environment in which we are raised thus plays a vital role in the development of our self esteem.  The ideal would be for a child to be bought up with loving, affirming parents.   ' I love the person you are'  and 'your viewpoint is valid'.
Unfortunately, many of us are reared in unhappy often dysfunctional environments,  where value is placed on what we do not  on who we are as unique individuals.  In consequence, from very early life,  fear of rejection, fear of failure and may other fears will result in us measuring ourselves by what others can see and value not by what we desire for ourselves.
Improving poor self esteem
The first step to improving low self esteem  is to review our lives (perhaps with a close friend or professional ) and identify  the reasons why your self esteem is poorly developed (or failed to develop). This assessment should highlight instances where we a) buried our self confidence in our own ideas and abilities and b) subdued or ignored our own desires  in order to please others. Failure to fulfil our potential in the early years of our life, can lead to lack of self acceptance, poor self confidence and low self esteem.
Once we understand why we have low self esteem, we need to develop a more compassionate, favourable and less critical view of ourselves.  Taking a step at a time, we need to reflect on who we really are, what we are feeling and what we want from life.  This activity will widen  your  prospective, the wider your prospective the less you'll judge yourself by  narrow criteria  like status, attractiveness or material wealth.  Instead your appreciation of your self will increase and with it  your self respect and self esteem.
High self esteem can act as a cushion,   helping us to  'weathering the storm' during times when life does not meet our expectations. Rejection, disappointment and failure (even our best efforts aren't always successful) are a part of daily life.  High Self esteem can help a person us get through difficult times.