Wanna improve on ur English? Read these:

Warning: Not for the faint-hearted.

To improve on reading and pronunciation: 

1. The sounds of English (Deterding & Poedjosoedarmo) 

To improve on English grammar:

2. The grammar of English (Deterding & Poedjosoedarmo)

To understand Singapore English so you can effectively 'code-switch':

3. English in Singapore: An Introduction (Low & Brown)

There you go. My year 1 textbooks from NIE that helped even ME, the Grammar Nazi. You have no excuse for having a lousy command of the language anymore.