FIRSTLY. I am in no way a high elo god and so whatever advice I have is not challenger material but it isn't bad either- I have a lot of experience winning games with Morde so maybe what works for me could work for you too :) (probably not in high elo though)

Early- Play aggressively against champions you can out duel with Conqueror but be careful of enemy champs with Lethal tempo or Conqueror as well. If you have a hard matchup like Vayne, just stay back and farm safely (wait for gank or play slowly to catch them out when you're near your turret).
Mid- By now you should have your mythic, tier 2 boots and one other full item (if all goes well). Look for 1v1's and take enemy jungle monsters if you've already taken the top turret. If you have not taken the turret yet, push your lane and chunk it down whenever you can but do not prioritise over helping your team (help secure objectives and picks- don't be greedy, let the others have kills too).
Late- You're likely a dueling nightmare by now, split push if need be but definitely help team secure barons and drakes by ulting enemy jungler to prevent smite steals for example.