This is how i use Darius . Hope you like it :D

Try using " e " to catch a enemy >> " w " to slow and other efects (i dont remember) >> " q " when he is try to run from you ( try using " q " wheen he is not too close to you to get aditional damage ) >> ( if cooldowns run out ) use " w " again for his efects >> keep the " e "
to use when he is trying to run >> " again " q " >> and in the end the ultimate " r " >> try always to finish an opponenet with your ultimate because of restoring the cooldown .
If you are cought with 2 opponents try reducing their life to 1/4 or lower then finish one with ultimate and the second enemy again with ultimate , so you score a double kill.