As the others have said no need to mix in a separate bucket first.
First, check you owners manual for system capacity.
Do your flush in whatever method you do. After the final drain, fill your radiator with coolant to half, (50%) the OM spec'd capacity. Then top with distilled water, drive some to open tstat. Check again and top with more distilled.
The one additional thing if you have a non pressurized recovery tank you, must drain it. I usually save a small amount of coolant after I've drained and filled to ~50% coolant in system and recovery tank. It usually drains some from the recovery tank after being run. I add the remainder/extra coolant and distilled to keep 50% in the recovery tank.