Natural (asking advice)

I would like some/your advice on/about...
Can/Could you give me some advice on/about...?
What would you advise me to do?
Do you think I should...?
What do you think I should do?
What should/shall I do?

Natural (giving advice)

I advise you to...
If I were you, I would...
The way I see it, you should...
Take my advice, and...
If you follow my advice, you will...

Formal (asking advice)

Could I ask your advice on...?
I would appreciate your/some advice on/about...?
What would you recommend?

Formal (giving advice)

I know it's none of my business,but...
I think you should/should not...