One way to strengthen your vocabulary is to correctly pronounce the words you already know and use.
Should your pronunciation be precise or "correct"? Frankly, it depends both on the circumstances and the particular word.
If you're in a casual conversation with someone, they probably won't care (or even notice) if you pronounce the second month of the year as "Fe-boo-ary" instead of the correct "Fe-brew-ary" (notice that there are 2 R's in February, and they're both pronounced).
But if you're giving a presentation to people for whom correct pronunciation is important (an audience of English professors, for instance). they might just notice — and care — if you pronounce it incorrectly. Or if you're being "taped" (audio or video recorded), pronunciation problems can be more noticeable. Worse yet, they're permanent!
So you have to decide if correct pronunciation of a particular word is absolutely necessary. But you have to know what the correct pronunciation is before you can make that decision. The following exercises will help you make that decision.