Summarize:

If you don't want to go over alone, have a friend help you. This can also be useful if you left any big items, like electronics, at your ex's place. If you had an extremely messy breakup, a trusted friend can even agree to retrieve items for you.  Make sure you pick the right friend to help. A friend who's prone to drama may be tempted to start a fight with your ex. Instead, opt for a friend who's generally cool and composed, even in stressful situations. If your ex is giving you a really hard time about retrieving your stuff, contact a friend or family member of your ex that you are on good terms with. They may be willing to help you. If your ex is present when you're over, it's best to minimize conversation. If you want to be pleasant, stick to small talk and simple questions rather than bringing up any major issues.  For example, ask, "How's work?" or make a comment on the weather. Avoid open questions and topics that could yield negative answers. Asking "How have you been?", for example, may lead your ex to talk about their difficulty with the breakup. They also may pretend to be fine to hurt your feelings. It can be hard to let go, and you may be tempted to linger at your ex's place and make a lengthy goodbye. Focus on the fact you're there to get your stuff and not address any lingering issues with your ex. As soon as you get through the door, start gathering your things and leave as soon as you finish. If you want to say a goodbye before you go, keep it brief. Now is not the time to drag up lingering resentments or talk over the relationship. Say something like, "I'm going to take off now. I hope you're doing okay." If the two of you lived together, or if you simply left a lot at their place, you may have to make more trips. Grab the absolute essentials, like clothing, on the first trip. Then, before leaving, talk over when you can come back to get the rest of your stuff. You want to keep things as uncomplicated as possible, and physical contact after a breakup can get confusing. Avoid things like a prolonged hug hello or goodbye. If your ex offers a hug or another form of contact, keep it as brief as possible.
Enlist the help of a friend. Make small talk, if necessary. Try not to linger. Make more trips, if necessary. Keep physical contact to a minimum.