That eyebrow arched just a bit further. Draco set his own wand on the bed, and took Harry's, turning it over in his hand to get the feel of it. Using a different wand was always odd. Jarring, perhaps, with occasionally unexpected results. He cast a quick levitation, just to make sure he had it under control, before returned his attention to Harry.
"Thank you." Head cocked, grey eyes considered Harry, Draco's lips faintly pursed. "In theory, Occlumency is simple. As I said, it is a fracturing of your mind, an attempt to take pieces of your life and place them within locked spaces so that no one else can reach them. However, by partitioning your mind and heart in such a manner, you can learn to school yourself so that these things no longer show in expression or in action. You create separate spaces within yourself, and you move between them. You will, however, find that it is jarring when two such are expected to interact."
Draco's smile was tight as he gestured at the door to the nursery where Alys napped. "For example, your intrusion in Paris brought you into a space normally kept separate from the space left to deal with Harry Potter. This may sound too analytic, but it is, quite frankly, the only way I had to survive childhood, and in particular survive the events that began when we were teenagers."
And simply this telling of that information was a beginning towards breaking down those old boxes, which had already begun to crumble. Draco wasn't ready to let the walls fall entirely; he wasn't sure he could survive that if they did. "So begin by preparing yourself. Visualize your mind as a honeycomb, with multiple compartments -- or however you prefer as long as you have many spaces to put things -- and separate out those things you need to keep apart into each compartment."
Draco listed some of those things, in case Harry wasn't certain exactly what he meant. "Not just memories. Compassion: lock it away. Your affection for Hermione and Weasley. Your belief in the DA. You won't be losing these, they will still be yours when you need them. But do not take them out unless you are in a trusted space. You will keep them locked from those who could use them against you."