All FIFO really means is that as you put new ingredients (or produce, frozen foods, leftovers, etc.) away, put them in the back and move the older ingredients to the front. For things like canned tomatoes, onions, and milk that you stock regularly, this ensures that the older products get used first. And also avoids finding that bag of squishy greens buried in the back of the crisper drawer!
We put our rarely-used ingredients in a separate place, and when we buy a new ingredient used just for a specific recipe, it goes there. Again, we try to keep the older ingredients at the front, theoretically ensuring that we see them and use them before their expiration date.
Besides making sure that older things get used first, this kind of cycling also makes you take constant inventory of what you have in your fridge, freezer, and pantry. When these things are fresh in your mind, you're more likely to remember to use them.
What other tricks do you have for remembering to use up ingredients?