Self-esteem is...a really difficult thing to have, honestly. I find that I fluctuate between intense self-loathing and general apathy, with the latter being more prevalent than the former now, but I can't say I've ever really felt good about myself, or like I've had any kind of value. I'm either a worthless piece of trash everyone hates or just a voice that nobody hears. People contradicting that only makes it worse because they're obviously only saying that because it either makes them uncomfortable to see it or because they're better than I am, which is precisely why what I think of myself is true, because I never do this.
It's not too surprising I don't have any self-esteem to speak of, really. My relationship with my parents has always been awful - I'm an accident, a disappointment, and a complete failure - and I've never had friends to speak of. The only people I believe may care about me moved to the other side of the country when we moved closer to them, and have betrayed me more than once anyway. I've been abused, ignored, and outright hated for pretty much my entire life. I have to take responsibility for a lot of it, because of course it's not just everyone else's fault, and that doesn't exactly help matters either. I probably deserved a lot of the abuse I went through as a child, and I certainly don't deserve to have any friends now.
My advice would be to stop caring. When you get right down to it, what other people think doesn't matter and only has weight because you allow it to have weight, the majority of the time people only think or care about themselves and won't give your presence half as much thought as you might think they do, and...well, there is enough in life to punish you and make you miserable that is beyond your control, so you don't need to add to it yourself. Get angry, and then get over it. If you can't have positive self-esteem, then don't entertain the concept at all, and refuse to allow other people to jeopardise this by simply not allowing them to have any kind of significance in your life. It's difficult, but cultivating apathy is far more consistent than building a fragile positive self-esteem that someone or something else can tear down with relative ease. Contrary to popular belief, apathy is not a negative state of being, and people aren't built to be happy all the time; anyone who tells you they're always happy and positive is a liar. If you can cultivate a general apathy towards life you will find that you will enjoy those moments that are genuinely positive more readily, and that more difficult things will become easier because you simply won't be as emotionally engaged with them as you otherwise would be, so you will be able to focus on coping with them rather than on panicking about whether or not you can cope with them, which you will do regardless because life moves on and just as people aren't built to be happy all the time, they aren't built to be sad all the time either. Your overall self-esteem might not be positive, but it won't be negative either, and I would say that is far more important.
In my experience, low self-esteem often comes from comparisons - other people always seem to be better in every possible aspect. They have better personalities, better lives, better...everything. A little mindfulness of your own thoughts can go a long way into dismissing them, or at least recognising that you choose how much weight you give them: this is something entirely within your control, even though it certainly doesn't feel like it. But feelings are often irrational, and you can choose to ignore them if you can recognise what they are and where they're coming from. People often boil these things down to very simple thoughts and ideas because they don't have time - or even awareness - to do anything else. Do some research into what self-esteem is actually composed of, look at each of these concepts in turn, then decide what they mean to you, and what exactly it is that you're not happy with. If you're that dead set on trying to be positive, identifying precisely what needs to be changed for you to achieve this is going to be your first step.
But always, always be mindful. I personally find optimism and positivity to be poisonous, because my mind just isn't built that way. If you try and force yourself to be positive when you don't feel that way, and don't believe what you're thinking, you are going to feel worse about yourself because you can't do it. But it is perfectly OK to not be able to do this, and it's not essential to better self-esteem. Life isn't always sunshine and rainbows, and that's fine. The key is recognising how that affects you, so that you can control your response and have it affect you in a less negative way.
I realise this probably isn't very good advice, but it's the best I have. I am a very analytical sort of person, and I find understanding something helps me to determine what to do with it.
