I came up with a method for summoning dream characters that's been pretty fool-proof for me.

I noticed a while ago that a dream has an easier time making things work the way you want if it's believable in the context of the situation.. but it only seems to care about the very last thing that happened. For example, if a character is chasing you and trying to murder you in a dream, all you have to do is say something like "Aww, so we're friends now, awesome!" and the dream responds to that context, forgetting the whole part where the guy was just about to chop you to bits.. and making him suddenly friendly.

So I thought why not use this principle to summon dream characters. So what I do is I pretend that I'm mid conversation with them. I'll just act as if they're in the next room and we've been having a conversation all along. For example's sake let's say the dream character is Darth Vader, and I'm outside my kitchen, and imagining he's in there. I'll just be like "So how those pancakes coming along Darth? They nearly ready yet?" "Oh sweet" etc until after a few of my responses, I'll hear the character respond. At that point, my mind obviously expects them to be in the room since I heard their voice coming from there, so now I walk into the room that I'm pretending they're in, and sure enough, they're there.

Of all the methods I've used to summon dream characters this has without a doubt the highest success rate for me.