Guilty of the fuel cap situation. During my Instructors course I was 10min into an exercise on airfield, and got a radio message from the tower "Helicopter XX, company message requesting you check your fuel cap" - they had found it on the pad
. I was new to refuelling the aircraft and thought that
perfect little flat on side/top of the fan scroll seemed a sensible place for it - not a good idea, ALWAYS put it on the seat so you notice upon embarkation if you haven't put it back in it's place.
Check the bottom of the rotor mast fairing as previously mentioned for any rippling or dents indicating mast bumping/hard landing, also re:hard-landing check that you can just fit your fingers (small ish) between the bottom of the tail boom and the top of the fan scroll. Whilst there obviously check the fan scroll nut is aligned with the paint strip, if not, don't fly it (overspeed).
A new one, from experience, is when checking the swash plate boot on the main rotor head you should feel a uniform circle of nut heads under the boot (approx 8-10), but you should not feel evidence of any other objects of un-uniformity. Somebody I know felt an unexpected lump in there, the boot was removed to find that after maintenance a bit of locking wire (steel) was left just touching on the thin aluminium plate (held down by the nuts), one part was stationary and the other rotates, and over a short period of use the wire had stripped off a circle of the inner portion of the aluminium plate, leaving what looked like metallic orange peel coiled up under the boot....
Check for smooth operation of the collective lever - if it's not smooth it could be indicative of overspeed (mis-shapen pitch change bearing I believe)
On the safety course they are very keen to emphasise that when belts are in their first hundred hours it is extremely important that you get blades turning in less than 5 seconds, otherwise the unpredictable slippage of sticky new belts could cause the belt to jump out of it's 'V' and become misaligned which has apparently been the cause of some incidents. Apparently on older belts it is more acceptable as they are less likely to randomly stick and jump out of the groove, but that assumes you always know how old the belts are, as the manual says, "blades turning... less than 5 seconds" if not - don't fly it.