If made 2 guides about 2 champions.
Darius is more Tanky and u should last hit ure enemies with his ult.
Darven is more the ad carry he has not mucth life so u have to buy a guardians at the late game, you should catch ure q to farm minions but if u chase some one dont catch it, only catch it if u can.

Darius ( more dmg ) :
At the end of the build u should buy and infinity edge .. but wait for they whole money to buy it dont sell ure lantern for the 1650 sword .. wait for 2700 thad u can sell the lantern and directly buy the Infinity edge

Draven:
Q: Ever catch it to farm, only catch it if u can if u are chasing someone.
W: U can activate it again if u catch ure q so if u can handle ure q u can chase some one and activate ure w all the time.
E: Ure e skill is good if u are chadeing someone, u can slow him and push him to the side.
But if someone chase u, u can also use it to push him away and slow him.
R: Ure Ult is good to Snipe if u can handle it or to last hit someone.

Skillorder: If u atack a enemie u should have ure q stact. So first farm minions and hold ure first stack of q, than attack and aktivate ure secound stack. If he runs away hit him with e to slow him and always catch ure q if u can to activate ure w again. use ure ult to last hit him ore snipe him if he comes aawy with lose life.

Darius:
Q: Ure q dose a lot of dmg, middlegame its good to farm minions becuase u nearly 1 hit them and if u want to kill its also dose a lot of dmg.
W: Ure W is a normal hit with more dmg .. its very good with a sheen because than it does tonns of dmg. U also can used it to chse someone becuase it slows and if someoen chase u u can slow him to.
E: ure E skill is pervect to pull some one in ure tower or in the Teamfight .. if someone runs away pull im to u. U also can pull enemies threw walls.
R: ure ult does true dmg and staks with ure passive. Do it to last hit enemies becuase than the cooldown will refrech.

Skillorder: First hit the enemie with w to slow than pull him to u with e hit him with q and again with w, if he is on low life last hit him with ure Ult.

sry for my english skills, im german!