Some good advice from Ben
I’d add that I have used zinser to prime a upvc conservatory, which we then top coated with an acrylic recommended by the Johnstone’s guy. It has been perfect for 5 years, so I am sure you will have good results on tiles.
Also good prep as mentioned
If you are doing a colour top coat, you can get a splash of tint put in your primer so you aren’t going straight over white. Johnstone’s or any decent paint suppliers will do this for you.. Really helps if painting over a white background as you can easily see where you have missed, plus it improves coverage