Yes, how could you forget lava? xd
Very good indeed, I think this is the best answer I have gotten to this question.
So, you'll need to keep this simple ideal of fire within you mind as you perform any fire jutsu, as this is the basis of any fire technique.
If you need to make the fire hotter, you'll add more fuel to it (Katon chakra) if you feel it getting out of control, suffocate it slightly to keep it inline by taking away it's chakra.
Now we shall begin by you holding out your palm, face up, then channel the idea I you have just told me about and focus your Katon Chakra into your hand, forming a small flame on it.