There was a post like this in the old forum and I found it really helpful, so just post any lesser known features that people should make use of or some tips that you should know. Here's some from me:
-You can hold a throwing knife/goggles in your mouth slot
-A facehugger can act like a very effective gas mask and protect a host from dying in gas as long as it's on
-Small objects can be stored in your helmet
-The ASRS system in req can be hacked just like requisitions consoles in regular CM
-The lethal injections in the brig are filled with quickclot
-Using a screwdriver on a door will make it impossible to pry open for xenos, similar to welding
-If you're standing next to an intercom you can use :i to talk to it without having to click it