Almost any steam iron is practically BIFL if you use only distilled water in it.

If you apply starch/sizing to your clothes, keep an eye on potential buildups on the hot plate, gently scrub them off with a generic magic eraser and rinse off the residue.

Don't let it fall to the floor.

That's about it.

For ironing boards, buy a quality pad. Don't let wet or damp items lay on the board repeatedly. When you're done ironing, if the pad feels moist, take it off to dry separately. These steps will keep the board from rusting.

Lightly oil the track the legs slide in.

These are simple devices that last a long time if a little care is taken with them.