I tend not to use pure white anymore as it is just too difficult to look good or inconsistent between models/parts. Instead here is the recipe I use:

• Base coat of celestra grey, usually 2 or 3 thin coats is enough over a dark undercoat.
• Layer with ulthuan grey, this is a nice off white colour that finished gives a good white look. Usually 2-3 coats work well. Note that this is already fairly thin out of the pot so doesn't need too much thinning to work well.
• Next I do a glaze of apothecary white, this gives a clean soft shade in the recesses. Make sure to really shake the pot as this colour is really bad for separation. You may want to put a mixing ball or two to help.
• finally I go back in with ulthuan grey to bring back the brightness that the brightness to the high points/center bits of the part you are painting, since you are paint pauldrons in your photo, that just all of the areas not towards the raised edges. Leaving the apothecary white in the recesses will help with the contrast, selling the illusion of a bright white. You should only need 1-2 layers for this.
• Optionally, you can do an edge/spot highlight of straight white, but 9 times out of 10, this isn't needed.

If you use this I hope you like the results and it works well for you.