urgent !!!! can anyone give me some importance typography rules that apply on the packaging design

Your question is too vague to answer. Can you be more specific?

But as natobasso said, it's a huge subject. What are you interested in specifically?

like hierarchy .........

Here's a few in general:

1. Use sans serif for titles
2. Use serif fonts for description text (unless you want to use a readable sans serif font)
3. Don't use more than three fonts
4. Avoid bursts like the plague, but sales guys love em
5. Do not use fonts in photoshop unless you need a heavily stylized title (with effects
6. Use typography appropriate to your packages contents (Trajan for DVDs, etc.)

and

7. Avoid knocking out white text in a black background that isn't title text.