Re: What is the best way to create fog\\smoke?
oklalawman has the story right on fog -- I also worked in technical theatre. I would advise Googling for smoke, fog and theater. There is lots of info out there.
To make things easier on yourself, be advised that in the real world and the theatrical world, smoke and fog are very different things with very different properties and uses. For the most part, they are like apples and oranges in the way that they behave.
If you want to shoot beam-shots close to the ground fog may be more appropriate, but I doubt it. Whether fog is man-made or naturally occurring, it is heavy and wants to be near the ground. It is very clean to deal with using variants on the method oklalawman outlined -- no poisons, smells or creepy residues -- but you'll probably have to stir it up a bit with a fan. Fog also dissipates very quickly and no matter what size you make your fog machine, the pause between repeat takes may be problematical.
Because artificial smoke is closer to room temperature it is much easier to disperse into a room in an un-stratified manner. Smoke is used much more at concerts because it gives the lighting folks more to work with.
On a side note, smoke can be made to emulate fog for a bit by cooling it down as it leaves the machine. This will make it hang closer to the floor.
I wouldn't use just any non-commercial agent to make smoke without quite a bit of research. Aside from weird toxic effects these agents will condense out ON and pretty much IN everything that they come in contact with. You probably don't want some oily condensate coating everything inside your laser, stereo amp, computer or TV. In nightclubs and theaters where smoke is used often it is very important to use an agent that will have minimum negative side effects (which can also include making the floors dangerously slick for dancers). Even using professional products designed with these pit-falls in mind these problems can still occur during long runs of very smoke heavy shows.