I like cooking with spices but I have no idea what I am doing when I do so

I have a reasonable understanding about how to balance sweetness and acidity. I have a good idea of how much umami to add (as much as possible, duh), and I can add salt to taste. Bitterness I just keep to a minimum.

But when it comes to adding spices, I have not been able to come up with a good method. I find that adding spices to taste is not very effective, because the flavors and spice level changes considerably as the soup cools down or as you mix the curry with rice. I also don't know how to make a spice mix that will blend nicely, and I never know exactly how much to add. I just roll the dice each time and hope for the best.

Is any of you a spice master? I am looking for tips about how to improve my spice game.