Having been to Lagos several times over the last 10 years, I concur with iaflyer:

If you stay in the crew hotel (probably the ***********), you will not need anti-malarial protection.

As a malarial precaution however (and his applies across Africa) wear long sleeves from dusk onwards when outside in the evening, use a mosquito spray and keep trousers tucked into socks to be 100% safe!

wrt to other precautions, iaflyer is correct, avoid local water and anything that may be prepared using it, including ice in drinks; wash fruit skins yourself in bottled water - to rinse off other peoples infections. It sounds unpleasant but is not that different to precautions you 'should' apply everywhere in the world - after all you don't know the personal hygiene regime of all restaurant staff, do you?

imho, in Lagos, the greater risk is when away from the hotel ie - en route to/from the airport and when wandering away from it on the slip! I speak from having had to swerve in the crew bus around decapitated bodies en-route from the airport!