How to center large figures in LaTeX and how to fix short justified lines?

I have 2 questions:

1. I am trying to center a figure in LaTeX, 开发者_高级运维but above a certain size it just starts at the left margin and goes beyond the right. How can I make it actually center, so the amount it goes over the left margin is the same as the right?

2. Some short lines justify to fill the whole page width, which makes it look really bad. Is there a way I can fix these lines, or maybe set the width for justification to be considered?

Thanks in advance.

1. That "certain size" is the \textwidth. In order to get defined centering behaviour, your elements should fit into that. You could adjust that width, or use something like \resizebox to fit your elements into the text area.

2. That is usually seen when you try to write paragraphs without writing paragraphs. You should provide an example so we can see what you are trying to do. Remember, paragraphs of text are to be separated simply by empty lines in the source.