The tip of pronouncing 'g' correctly is:
First the back of your tongue reaches up to touch the soft palate. Then you lose the contact between them and the same time blow out the air lightly to make the sound.
As for 'k', the method is the same as 'g'. But the air being blown out is stronger.
The tip of pronouncing 'h' correctly is :
Pull back your tongue, letting the back of your tongue reach closely to the soft palate; then blow the air through the gap between your tongue and soft palate to make the sound.