I've just decided to go through it and highlight the changes I would make in light green. Hope it's helpful.
He slowly advanced through the foliage, drawn by the sounds of combat and the slight hint of blood on the air. He stopped for a moment as he heard the familiar hiss of a blood drinker. Slowly, he advanced on the clearing ahead, expecting to find the remains of a rather unfortunate guardsman. Instead he saw something far worse. He watched as the lictor jumped from the tree, acidic slime eating away at its flesh [not specific enough - is it the own lictor's flesh, the human's or the tree's bark?] and watched [used 'watched' once already - try gazed, regarded etc.] as its primary eyes melted into slag [what's that mean? Try and be more specific]. The enraged creature charged forward towards a fleeing figure in the distance. He quickly fell back into the foliage to go around and see if he could aid the poor human. He moved silently through the foliage of his home world, knowing a fellow catachanís life was at stake. He carefully stepped over the roots of a large tree and looked into the clearing. He realized right away that he was too late. He [You use 'he' an awful lot - maybe you could give him a name or refer to him differently, like 'the soldier' or 'the trooper'] watched the lictor as it ate the catachan fighterís corpse piece by piece, starting with the head. He slowly [same adjectives again - try gradually] stepped backwards hoping to make his way back to the scouting outpost. He knew he would do more good warning of the coming swarm then dying to avenge a fellow warrior. He reached behind himself; reaching for the trunk of the old tree. The moment he felt it he grabbed hold and flipped backwards into its lower branches. The entire time he climbed he watched the lictor feed, waiting for it to hear him and inevitably kill him. Once he had reached the top, he readied himself for the jump to the next tree. Then he heard the sound that he had been dreading, the snap of a twig. He immediately jumped to the next tree, turning as he did to watch as the lictorís claws cut effortlessly through the trunk of the tree where he had been standing. He hit the next branch hard and slipped, crying out as thorns growing from the branch stabbed into his hands. He let go, knowing the lictor was already leaping for him. He waited as he expected to hit the ground; then he realized the thorns were holding him up, slowly cutting him from palm to fingertips. He swung himself so that his feet were against the tree and pushed off hard, finally falling to the ground below. The whole incident had only taken a moment, but it was still too long. The lictor twisted its head as it leapt and flesh hooks began flying towards him. He tried to dodge them, but was hit. He struggled to cut himself free as his world began fading and changing colors. The lictorís poison was already starting to kill him. His senses began dulling a fading [doesn't make sense]; he felt a feeling like he was being pinched on his arm. He looked down and realized that another flesh-hook had hit him in the arm [just get rid of that]. He slowly fell to the ground as the lictor climbed down the tree. He hit the ground and moaned as his world faded to black. His last thought was that he had failed. He had failed. [Doesn't really work - suggest something about his comrades and the outpost instead].
Overall I'd say it's an improvement from your last piece, but you're repeating yourself quite frequently. Try and vary your adjectives more, and also use other personal pronouns rather than 'he' and 'him'. Finally, reading one big chunk isn't as pleasant for the reader as a piece of writing in paragraphs is. When plausible miss out a line so that the reader enjoys it more and the story simply works better. Nice job though, keep it up.