To experience Introverted Sensation:
• Pick a category of object and practice spotting it in a crowded room. Not something easy like a color, something you have to learn how to identify. For example, learn how to recognize cotton and distinguish it from other fabrics, and then try to spot all the cotton garments in a room full of people (or in your closet, if you don't want to embarrass yourself). Alternatively, learn how to identify several species of tree that live in your area, and spend an hour or so walking around identifying each kind of tree that you come across. Other possibilities: models of cars, breeds of dog, categories of differential equation. In other words, through deliberate practice, become an accurate recognizer of specific types of object, so they "jump out at you" in the midst of other things.
• While driving on a long trip (in the U.S.), note all the out-of-state license plates you see. Stay focused. Carefully check every car as it goes by. Notice everything you can about each state's plates: state mottos, colors, placement of text, pictures, any other special differences. For the full effect, write these things down in a log book.
• Do a Where's Waldo? book. (Might be too difficult to really work as an exercise.)
To experience Extraverted Sensation:
• Walk around downtown in a city during the day, when lots of people are around (even a small town will do). Note what gets your attention, and what kind of attention it gets. Just walk around and let things grab your attention. Don't be deliberate. See what's exciting and what's boring. If a place looks exciting, go inside. The second you feel bored, leave and look around for something new. Don't think about this, don't reflect on it as you're doing it, and don't think ahead. Just go with your immediate gut reaction moment by moment--enter or exit the store before you have a chance to entertain a second thought.
• Walk again, and this time note what's grabbing other people's attention. Where's the crowd?
• (An exercise for brave people.) At a party or a bar or some other gathering of people, attract as much attention as you can to yourself. Anything that works is acceptable: feigning a heart attack, dressing better than everyone else there, dressing in a different color than everyone else there, putting a lampshade over your head--whatever works (it doesn't have to be dramatic, though, especially if you're just testing this out). Keep one eye on how much attention you're getting, and what kind of attention. As you try this at different gatherings, practice getting specific kinds of attention: intrigue, fear, disgust, sexual, laughing at you, laughing with you, etc. Cultivate some techniques for gaining specific positive kinds of attention. You will notice that you need to adjust your approach to fit your audience. As you practice, you'll develop a sense for what "plays" and what doesn't.