Entering minds is most easily done when the host-to-be is either asleep to within their headspace. When inside the host's mind, one can walk around between memories and bunches of knowledge that the host has gathered.
When someone is incredibly overwhelmed by emotions and thoughts, one of the outcomes is that they retreat into their own headspace and enter a sleep-like state where they are unresponsive to stimuli. This has been theorized to happen in order to block out the possibility of even more stressors when they're already overloaded by internal conflict. Some headspace-bound people have been able to reflexively respond to stimuli, and some of them recount experiencing sensations or encounters in their headspace similar to sensations their bodies have been exposed to and voices nearby.
Headspace-bound people may either come out of their headspace on their own, but the chances are much higher if someone else enters the headspace in order to help them out. Assistance also lowers the risk of the person losing their emotions, among other changes, if they happen to exit their headspace on their own.
Other people are able to enter headspaces through a combination of the state of their own minds and control over their magic/soul. Those with a more open mind -- one that is more understanding of or willing to understand the host-to-be -- will face less resistance from both themself and the host. The ability to direct the energy from their magic and/or soul toward the person also aids in the transfer of conscience. The body of the person going into the host's mind also goes into a sleep-like state, although they are unable to recall or feel stimuli that their body experiences while in the other's mind.
People with a lot of creativity or dedication to their own thoughts have also been able to enter their own headspace without an overwhelm of emotions or past eventss to process. In those cases, the access of their headspace is resctricted to those thoughts and whatever their creativity is directed at, and they're much more responsive to stimuli to the point of being able to be brought out of their headspace by it.
Faded Dream of a Psychomeddler backroom labyrinth Eternal Echo of the Thrilling Tour-our-our