Touch is Key

Part of what makes a couple a couple is that they are "within each others private space" - that is, they are comfortable with touching and hugging. This is one of those lines that tends to be drawn between a couple and random strangers. So ensure that you maintain that distinction, by touching and hugging your ex. Just because you have broken up should not mean that you suddenly don't care for each other any more. The more you can maintain those subtle touches, the more you can help rebuild the chasm that appeared.