They should have come of age.

They should be of sound mind.

They should not be under bondage.

They should be males.

They should have the ability to carry out the Jihâd with their limbs and wealth (such as possession of good weapons).

As for what are imperatives thereof:

Good intention (to exalt Allâh's Words).

Obedience to the ruler.

Not stealing from the war booty.

Respecting the terms of treaty (with the enemy).

remaining steadfast in the battlefront.

Avoiding corrupt practices.

There is nothing wrong in fighting behind a sinful ruler (so far he is a Muslim).