Well the best way that I know how to deal with ADHD as I don’t take any more pills to help with concentration, is through meditation and in order to get there especially if you have a hyperactive mind I found was to take a lot of walks or do some sort of physical exercise before meditating. If you skip that step or can’t do physical exercise for some reason then they key is persistence just doing something until it clicks for you.
There are several meditations out there that’ll really help with calming and focusing your mind if that’s needed, if images keeps popping up review this post first regarding correct breathing, like the poster I had problems before I found out somewhere that breathing is a very important key component, when meditating, and then return to your meditations with this concept in mind to see if it helped out in some way.
I think in addition to calming your mind I wonder have you or are you developing your astral senses? Like clairvoyance, clairaudience, etc? Because if not that’s an important thing that’ll really help the evocation process along.
If the I suggested was irrelevant or not of use, let me know what kind of info you need and I’ll see if I can help you out in some way.
Good luck.
Teras390