Well, fire is many things. Is destruction, chaos, war due to its ability to burn. Also is light, heat, power, energy. It can be used as a very good protection and attack. The fire is weak against water, but strong against wind. Fire is also related to the eternal love, a flame that never extincts.
Stop right there...fire is not simply destruction and power. It is life...it breathes, grows, consumes, and feels. It is like a heartbeat gently working till it is put out naturally over a long period of time or till the rain mollifies it. That is Fire's nature.
Feel the chakra within you and picture fire spreading and consuming, but feel it's presence in yourself as well.
Uh-oh, ok.... *goes under a tree and practice with the leaf for two hours, until half leaf burns away* WOW! that was great ! Now, lets go for the other half...
*Half an hour later, the leaf is ashes now* At last... Now what sensei??
.. Ok sensei...
*with my hands in the tree, i focus my fire chakra in the tree and concentrates, and in 3 hours, the tree became ashes*
Ready sensei What's next?