I wasn't too sure how to make damage more apparent, could add subtle screenshake or impact frames or something? With the blood droplets it's easiest to get them while the enemy is dying, as they spray out a bunch of them during their death animation. If there aren't any other enemies nearby you can actually just stand on top of them and get a bunch of free health. The grenade is also great for getting blood fast, you can bomb a big horde of enemies and stand underneath them, there are also stationary enemies later in the game that are basically free blood sources.