The IR film is sensitive to visible wavelengths too---actually far more sensitive than it is to the IR wavelengths. You want to expose it through a filter so that the film is "seeing" *only* the IR; otherwise the image is dominated by ordinary visible light, and the result doesn't look like anything special.
Originally Posted by AutumnJazz
On choice of film, I haven't used the Ilford because its spectral response doesn't look very promising. I've shot a fair amount of the Efke (and the old Maco 820c, which I believe was the same emulsion on a different base) and absolutely love it. 6 ASA seems about right, although I've been able to rate it higher and get some nice images at the limits of handholdability.
I haven't shot IR in 35mm in several years, but my recollection is that the meter on the camera (a Bessa-L) produced decent results if I set it at 100 ASA and metered through the filter.
Infrared is really fun. It's challenging to find ways to use it as something other than a special effect.