Every Singapore diver has done at least one of these. Here they are, ranked by how much they cost me in comfort, not gear.
1. Overweighting yourself. Hantu isn't cold. You do not need seven kilos on a 5mm shortie. Try one kilo less next dive, you will thank yourself at the surface.
2. Ignoring the current. The tide moves fast here. Check slack water before you kit up, or you will be finning like your life depends on it.
3. Diving without a torch. Viz sits between 2 and 5m most days. A small dive torch turns "this is depressing" into "look at that nudibranch."
4. Skipping the pre-dive briefing. Boat crew know where the current is going and where the fish are. Listen.
5. Bringing a camera on dive one. Get your buoyancy dialled first. Cameras magnify every bad habit, and Hantu's silt is unforgiving.