God does not need principles to bless you. After all, he causes the sun to shine on believers and unbelievers alike.

God is a giving God and if He could give you his son, there is nothing He would hold back from you. God cares about your well-being and He wants you to prosper. He is moved by your tears, what kind of a father will not?

The only principles that should drive your prayers is the love and relationship you share with God.

You may ask then,

"How long should I pray?"

Pray till you see the answers to your prayers.

It may take some time, but think of it like pap, you just need a little more hot water for it to form perfectly.

Don't give up stirring till it's formed.

Pray till you see the answers to your prayer.