Now, I'm no strategy god, but listen to these no-no's for humans (and aliens)

1. If human, refrain from using your blaster. Ever. The only exception being baiting. This only gets worse if you use a blaster within 30 meters of an alien structure. You will fail to scare a Dretch with that crappy little thing. And, worse, fail to kill him. I tested this tonight, as the Dretch. Fed*.
2. If alien, don't hide in a corner unless you can get out quickly. I experienced this with a shotgun. Bad day for my poor Dretch. Rest in pieces.
3. If human, always buy armor. Stay at home if you have none until you can afford it (by time or by defense kills, three humans will bring down any S1 alien even if just with rifles. Five with blasters is a safe estimate). You will feed the Dretches if you enter an alien base with no armor.
4. If human, always stay away from the aliens. They will hurt you worse at close range. Even Advanced Dragoons will hurt worse close-up.
5. If playing as an Advanced Dragoon, humans never expect a snipe.
6. Never battlegrange. You will epic fail, unless you meet specific criteria (One of three ranged attackers, one of two with projectile attack) necessary for your mission.
7. Always stay with a teammate if you're still using a Rifle (with no armor) or a Dretch. You don't have to be too close, but all but the most suicidal (or pursued) Dretches will avoid two blue blips.
8. Turrets are your friend, as are Acid Tubes.
9. Boosters hurt humans when used by aliens.
10. Aliens should always stop by a booster.
11. Always upgrade at the first possible chance if human. As alien, be cautious, Basilisks are notoriously hard to play as.
12. Advanced Dragoons are better for human-familiar players than Tyrants.
13. Avoid twitch shooting with the Advanced Dragoon. You can (I have) killed an ally in a tight situation.
14. Painsaws are fun, but are not for everyone at all times.