Of course, it changes from person to person,
[and I have yet to find mine]
but I've read several different techniques.

Such as, summoning a door, and telling yourself [or saying out loud] that your dream guide will be behind it.
You could also just turn around, telling yourself your dream guide is behind you, much like if summoning a normal DC.

But I've heard that often, nothing will work until the time is right.
So if you're having troubles, don't worry,
you'll find your dream guide when they believe you are ready
^__^