Beware the beginning of this level. You have some spiky creatures and a power switch. You hit the switch and you will have to fend off the creatures. I advise that you ignore the switch if you don't need the practice.
There are three squaddies at the end of this level and one placed dangerously at the top of a pipe (grab the shell from the area right before the shallow water - use this to kill the squaddie at the top of the pipe). Either aim to jump on or under him.