I don't s see much about invocation in modern practice anymore. This is sad to me because invocation is one of the things that I found to be supremely transformative for me.
Invocation is the process of taking into yourself a spirit. Not the same way as possession, where you step aside and let the spirit take control, but in a way where the two of you kind of cohabitate, if you will. It's… stepping into a spirits energies. I think of this like putting on a mask or assuming a character. Keep in mind that this doesn't make it fantasy. Properly rooted, this allows for real energetic shifts. See my article on magic and play for more on that.
Sure, this is a process that can be compared to acting, but good actors will talk about the character as if they're real. Like they share that on screen time with someone else. That's what this is all about. A good, deep trance state is useful for this, especially as you're first beginning to learn this.
I tend to symbolically use either a physical mask, or at least the symbol of putting on a "mask" to trigger these kinds of things. It functions as a trigger for internalizing that energy, that also has a way to turn it off so to speak. You'll put on or wear your spirit in many ways.
Absolutely this is a fake it until you make it thing. As you practice this, you'll start to feel the difference, but even before you can feel it, abandoning yourself to this will allow for real changes. This is one of those areas where when it's working, you feel it, but the only way to start getting it to work is to do it.
This is almost purely a mental thing, at least to apply day to day. It's about gathering the energy that a spirit carries with it, and putting it on, and then trusting that. Relax into this, and it's exactly as simple as it seems.