Bidding (I'm sitting South, play 2/1 and East's 2D is weak):
W N E S
- 1C 2D 2H
3D 3S P 3NT
P 4D P 4H
P 6H =
Opening lead is ♦3.
I want to take this hand as an example to ask expert's thinking process from first trick. Knowing how to think is more important than only knowing how to play a hand.
I was always lost my head if i got a hand like this. Normally i can handle a hand relative to a single playing skill, like avoding a dangerous opponent, endplay, squeeze, safe play and etc, but i can't handle a hand like this, it's about combining of different chances, reading form bidding and play, handling possible bad distribution. I know i have to consider all these if i want to play well, but when i really try to do it, i was defeated more than i succeeded.
So, can you give me your thinking process on this hand and do you have any advice on me?

Help
