"My advice is simple."
Translation:Mon conseil est simple.
I was always taught that "un conseil" was like a singular piece of advice, and "des conseils" was like advice in general.
Difference between advice and opinion:
Statement: it is hot today
Opinion: It won't last, I feel it.
- Advice: Don't forget your hat and your sunglasses
'mes conseils' is authorised by Linguee and is, surely, fine here since we do not know, in context, whether the advice is specific or general.