Preparing concrete garage floor before painting

I've bought Ronseal Diamond hard garage floor paint.

Apart from heavy cleaning, what prep does the floor need to get a good finish?

I've seen "Sealocrete Concrete Dressing" at SElco which looks like it would be suitable. Anyone got any experience with such a product?

Anyone?

I'd always use a concrete sealer before painting garage floors.
Only done three. The first one I didn't seal it first and the paint can be scuffed/chipped off where it hasn't adhered sufficiently. This was a new concrete floor.
The other two that I used a sealer first, one was a very old concrete floor and the other was new concrete. Absolutely no scuffing/chipping, etc.
I applied two coats of sealer. The paint goes on easier and you'll need less.
As for preperation, just sweeping, or better still use a vacuum, 'cos you'll always create dust from an unsealed floor.