Okay so, when you vampirize someone energetically - how do you know if you’ve been successful in doing so? Do you feel a physical difference?
That all depends on you and how you feel energy/chi/prana/vital force/etc.
As long as you can establish and the cut a connection, there will be some energy exchange.
When I take energy from something, I can feel it moving though the established connection or into me. That feeling came with time and practice, and constantly working on my technique. There are a lot of times where I am ‘unsure’, but I don’t let that stop me. I just keep on practicing what I practice.
Breathing in energy is a common technique. There is nothing wrong with it, and if you practice with it enough, you will become proficient. Do what you feel is easiest for you, and build on that confidence with practice.
Practice with objects and things. Practice with ‘empty’ space.
Those are simpler things to connect with than people. That way you can get a good feel for your own technique and know ‘for sure’ what it feels like to connect with what. Of course, connecting with a rock and connecting with a person will feel different, but you will ‘know’ and notice and eliminate your own doubt that it has happened.
Something that helps me, when I really want to fuck something, is visualizing myself actually reaching into them, not with a tendril, but my actual hand. Squeezing and taking the energy from the organ that I am targeting. To me, there is something more affirming and dominating about it than just poking them with an energetic tendril or seeing their energy being drawn towards me with each breath, etc.
A lot of vampire stuff out there is highly visual, but it doesn’t have to be.
If you get good enough with just perceiving the energy, you can draw it towards you without visualization.