How to meet a friendly poltergeist
Drop the term poltergeist, and also every other term that gives an emotional slant to ghosts. If you just refer to them all as ghosts, then we can concentrate on the matter and not the term.
There are ghosts all around us, all the time. It is just that they exist on a parallel plane to us. So, to see a ghost, you need to cross that line and enter the plane where ghosts reside.
Pick a day when you have lots of time. Turn off all electronic devices. Make a cup of tea or coffee. Relax. Close you eyes and think of a recently departed person you know. Let your mind just float around and do not try to find anything. What ever comes to you is relevant, but you might not connect it right away. After some time, go about your normal business, but keep a little space inside you to receive messages or just to think.
Repeat this process many times. The key is not to rush and not to expect anything to happen. you will realise that your own perception starts to change.
This is all i can tell you without meeting you.