The glass on my 400W MV lamp has gotten quite dirty lately, and i am thinking of washing it. I’m just wondering is it safe to use a cloth/paper towel and water on the glass without harming the bulb? Is there any precautions i should take? Thanks!

I assume you mean the lamp itself rather than the fixture. Yes, it will be ok, as long as you take care around the etch, it's all too easy to wipe it away if you're not careful. Keep water away from the cap area as well, it could seep in where it's not wanted around the electrical bits   

If it's really dirty, use isopropyl alcohol, but keep that well away from the etch, or it'll be gone..!

Standard glass cleaner like you'd use on your windows works very well for cleaning lamps too
Have cleaned many fluorescents that way.


And ofcourse this should go without saying, but...
Don't do it with the light on! Make sure it has fully cooled off before attempting to clean.