1. Search each room thoroughly before moving on to the next room.

2. Before moving on to the next room, press 'H' to know where to go
to progress on the main mission. Go to the place opposite fo where
the objective helper points you.

- This is for you to collect everything that
can be collected before the mission ends or before to places where
there is a point-of-no-return.

3. Use the Stun Gun as much as you can.

- You might find yourself unlocking achievements, well... you know.

4. Don't Buy The Auto-Heal too Early In The Game.

- Finding yourself wounded and having the opportunity of using those...
healing pods or whatever is an advantage and again, you'll unlock
an achievement for using those healing what-s 20 times.

Edit: Auto-Heal can be turned on or off in the options. So you can
disregard this quick tip.

5. Grind on Biohazard and Survival modes.

- Yep. They give a lot of credits and gold, relative to their short durations.

6. Make Use of Bullet Time and Devastation.

- Don't let pride or being forgetful take over you especially when
your survival is on the line.

7. Beware of Them Zombies Throwing Grenades.

- You read that right. Zombies throw grenades here. They can one-hit you.

8. Point at Their Heads

- And enjoy. :)