Where can I learn about usage of words?

I am trying to improve my vocabulary & English usage in general. To improve, I mean, learn & understand meaning(s) of new words, and know the usage & connotation of words. For example, “audacious” means bold (or recklessly bold), and is used in negative sense. How should I go on building a good vocabulary? And, able to use it properly?

I will list down some points, where I think, I need to improve upon and where I would need your advice.

1) When I read English newspapers or books, I come across some sentences that I fail to comprehend. I look up words in dictionary, and even after understanding meaning(s) of the word, I don’t understand it completely. For example, a tall order, reservations in minds, invalid ill, etc. I fail, may be because, I don’t know other meanings and implied meanings of words. I work with popular one or two meanings.
2) Use & meaning of quotation marks, for example, in news headlines such as : Police identify 42 Maval ‘Conspirators’ (appeared in August 14, 2011, first page, lower half portion).
3) Correct use of comma (,) & inverted comma (;) in sentences.
4) Writing essays or reports. I wonder which words correctly fits in a particular sentence. Also, I find difficulty in starting & ending an essay (introduction & conclusion).
5) When to use “a, an, or the” and when not to, take for this case the above sentence : Also, I find difficulty in starting & ending an essay. Is it right to use “an” here or not?
6) Phrasal verbs. Example, meaning of “give” & “give up” are completely different.
7) And, some general doubts like when to use word “awesome”? What does it mean exactly? Can you give some examples (on awesome/awful/awfully)?

I don’t expect you to answer all of the above doubts, you may elucidate (I guess, I am right on this choice of word) one or any number you would like to. I thank you in advance.