What should I expect visually when shooting Ilford SFX infrared film?

You will be photographing things that reflect near IR light well.
You are not photographing things that are 'warm'.
If you are not using a red or deep red filter, the things that reflect near IR will will have a fuzzy glow to them.

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Alfred SFX has sensitivity out to 740nm (compared to about 650nm for most other black and white films). (data sheet - always a good read)

As we humans can't see in this range (our vision starts to become much less sensitive in the 650nm+ range) we have to guess based on what we know of IR sources and reflectivity.

Living foliage tends to be highly reflective in IR. The clear blue sky is rather dark in IR. Clouds, are very reflective. And so on. This comes with experience in using the film and looking at other photographs and working backwards.

If you shoot without a filter, some of the image will be blurry. As IR light and regular light focus to different points, you just won't be able to focus for both at the same time.

You may wish to consider using a red to deep red filter which will increase the relative light in the infrared end and allow you to get a sharper image (focusing for red and IR rather than greens and blue). If you have a manual focus lens, look for the symbol on the focus for the IR adjust.

In this case, the camera is focused at just past 30 meters. To adjust for IR, move the red dot to the spot where the red line is currently. One could also stop down to about f/16 and hope for the depth of field being sufficient, though this may lead to some rather long exposures when combined with the filter factor for a deep red.