Regarding the wobbly lines, just keep practicing. The more you draw, the more steady and confident your lines should become.
As for improving, it takes a while and it's gradual. If you want to improve and you keep practicing, you will. It's all a matter how much hard work you put into it. That said, get to drawing from life. Study proportions, perspective, color theory, etc. And don't just rely on anime/manga as a learning source. Anime/manga, while greatly varying in terms of style, is always a distortion of real life (really, unless you're drawing from life, you're taking what's in your head and putting it on paper). You can't properly distort something if you have no idea how it really works, can you?
Oh, another tip as to how to check if something looks wonky, try flipping the paper over and looking through it with a light. Flipping images helps point out any obvious errors that may trick your eye at first.
As for improving, it takes a while and it's gradual. If you want to improve and you keep practicing, you will. It's all a matter how much hard work you put into it. That said, get to drawing from life. Study proportions, perspective, color theory, etc. And don't just rely on anime/manga as a learning source. Anime/manga, while greatly varying in terms of style, is always a distortion of real life (really, unless you're drawing from life, you're taking what's in your head and putting it on paper). You can't properly distort something if you have no idea how it really works, can you?
Oh, another tip as to how to check if something looks wonky, try flipping the paper over and looking through it with a light. Flipping images helps point out any obvious errors that may trick your eye at first.