Have ya tried japa meditations with a mala? It gives the brain and body a focus that it can dig into to.I’ve found the mix provided by kunda yoga of mantra, mandala(sigil) and asana the mind and body a cooperative focus so it can flow from state to state.
Connor posted an method is similar here, with a lil tweaking of the target it can be used for invoking many different energies not just spirits.