Start by slipping friendly and subtle reminders into everyday conversation, in order to let the person know that you would like your belongings back. This can be a casual question, like “Hey, my purple shirt is with you, right?” or more of a friendly joke, like “I see my shirt has grown very attached to you”. This will serve as a casual, good-natured reminder, and open up a gateway to friendly conversation on the subject.
If your friendly and subtle hints do not seem to be doing the trick, try being firm in your demands. Since it is your possession, you have every right to ask for it, so forego the hints, quit beating around the bush, and state firmly and politely that you want your possession back. Let the borrower know that the item is valuable and important to you, and that you need it back as you plan to use it.
By this point, most borrowers will be embarrassed enough to return the item – however, if you have a particularly stubborn case on your hands, or are dealing with someone who is not particularly concerned or responsible, take the matter into your own hands. Let the borrower know that you will be dropping by their house to pick the item up at a particular time on a specific day, and ask them to have it ready by then.
Finally, if all your efforts fail, exercise your legal right in order to ensure that your belongings are returned to you. If the borrower adamantly refuses to give the item back, the action is akin to theft, and requires that you take legal action. Let the borrower know that you plan to contact the police, and if they still refuse to return the item, go ahead and lodge a report with the authorities.