You don’t, really. No one can know the mind of God.
We do hear in Ephesians 2:8–10 that God has designed us for acts that we encounter on a daily basis, but Ephesians doesn’t include any advice on learning how well we did, or even IF we did.
That’s why one should trust like a child, with a child’s simplicity of heart, and keep oneself open to the immediate circumstances. That is key.
As to doors opening and closing, try not to look behind them – there is no “man behind the curtain,” only God Who has everything already mapped out.
Oh, and Another Thing 