How can I get my grenades to land where I want?
Aim short, or aim for debris/walls near the enemy so they stop and catch the target in the blast. For what it's worth, I was able to lob grenades with pretty good accuracy directly into the enemy's face by the end of the game but often times it was better to land it at their feet or something that would stop the grenade and catch them and everything with them in the blast.
You could always try aiming your gun in one direction and then throwing your grenade after you're done aiming. That way your grenade will go in the direction that you want it to go :D