Below is the procedure I use on all vehicles. It completely removes all old fluid, minimizes the amount of tap water in the system, and provides a reasonably close 50:50 mix. Use shortcuts as appropriate for yourself.

1. Drain fluid - radiator and block
2. Remove thermostat
3. Reinstall thermostat housing and upper radiator hose
4. Disconnect upper radiator hose at radiator
5. Flush system with garden hose through upper radiator hose until water runs clear
6. Start car so the engine can flush the water pump
7. Disconnect heater hoses, open heat valve
8. Flush heater core
9. Flush overflow tank
10. Drain as much water as possible from cooling system
11. Siphon water from overflow tank
12. Flush residual tap water from system by replacing it with distilled water
13. Again drain water from system
14. Reinstall thermostat
15. Button everything back up
16. Refill cooling system with specified amount of antifreeze calculated from the system capacity, bring up to level with distilled water
17. Run car, top off coolant with water
18. Keep adding water as required every morning until system is topped off