Steel french press, burr grinder - how to make nice and not bitter coffee?

Hello,

So I have a big steel french press, it comfortably makes two full mugs and its full capacity was listed (by the seller on Amazon) as 1.2 L. I really like steel because glass cracks easily in the dishwasher.

I also have a Krups burr grinder. So I expected some nice coffee - but am failing to make it. Instead, it's either watery or bitter.

The Internet (tm) says use coarser grinds, somewhat large amounts of coffee, limit brewing to 5 minutes. But it gets bitter. Smaller amounts with a coarse grind get watery; with a finer grind, bitter again.

I did also start preheating the steel french press first by keeping some freshly-boiled water in it, covered, for a minute while rocking the press. Things got somewhat better but not a lot.

So what's the secret here? How can I work out the formula for coffee that would be full-bodied but not bitter?