Advanced technique:
Try to move past the human and then attack. I call it the
run down. For example:
You start here 
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Run in the human's direction but focusing on dodging his shots and getting past him.................................

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Once behind, go on the attack yourself...........................

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This is very simple but requires some basic tactics. The ability to wall climb, wall bounce, pounce, and trample are essential. Dodging and refraining from attacking is needed, most don't run down humans because they are so tempted to go for an easy kill. Finally, understanding the terrain and turret placement makes this effective.
Once you get behind the human, the strategic elements begin to work:
- The alien (you) are between the human and turrets
- The human can no longer retreat to defenses for protection
- The terrain advantage is gone
- The human is fighting away from teammate support
This is all simple but it works with any class and most any human. Most beginners will simply continue to back up and land directly into your attack. An experienced player will either try to get back on the other side and retreat or fight from the new position. But for a second, the alien has turned the tables. By mastering running down a human, you can apply this with teammates.
The block is when you run down a human and have them outflanked by a teammate. For example:

You

Teammate

Unlucky human
Here is how the block plays out 
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Now, you pounce to get behind the human 
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Now close the human into the trap 
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All you have to do is stand opposite of the human's position. You will keep him from retreating and force him into the tyrant. If the human back peddles or tries to retreat, he falls into your attack. If he advances to avoid you, your teammate will finish him off.
Both you and your teammate can attack without damaging each other, if you both hold your positions.
The block is very effective because most large aliens end up teamkilling each other when attacking a human. So, by blocking, the aliens can position themselves to avoid accidental damage and ensure the human dies. Good players usually can play along with a block, therefore only 1 person (you) need to know what is going on. Just avoid going for easy kills and set up the trap.
A common situation to use a block is with corners__________________
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(you)
| .
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(teammate)
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Just hold your position and let the human struggle.