I wrote this little thing a while back and because I don't think it's quite a guide as I don't tell you how to do anything, I'll post it in general discussion instead. It's just some of my thoughts about possession and switching as well as some tips and tricks. Not entirely sure if I got something else to add, but it's pretty late right now and implying I put effort in stuff. Because this is posted in this section of the forums, how about others share their tips or problems about possession and switching here as well. Anything goes, really. Tell us what you have learned, what made it happen to you and what you think about it.
Possession
There are countless of methods people do to achieve it, but in the end, what matters is that you achieve the following: the host lets go of the physical body's control and the tulpa takes it instead. Ultimately, there is no one way that works for absolutely everyone, as our minds and mindsets are different. Symbolism can be a great help in getting started, as it can put you in the correct mindset right away if it's one that works for you well. It is all about your mind.
For hosts, letting go can often seem difficult or almost impossible. It might help to not see the body as "you", but instead as of some kind of vessel you just happen to control at the time and you can let go of that control, just like how your tulpa is there in your head but not controlling the body right now. Any way of making yourself realize you can sever the connection to the physical body and then doing it means you are on the right path. It's not honestly any more complicated than that, but it requires the right way of thinking and enough willpower to make it a reality. The actual method is up to you, do what you think feels the best. Relaxing all of your muscles and then concentrating on what feels different instead of what feels similar might help your confidence. Remember to talk with your tulpa as you are learning to let go, in case they might have something to say about it
For tulpas, it's nothing more complicated than just taking control. The physical body might feel different to what you've used to, but it just takes some practice to get used to it. Sometimes it can be tricky to get in control, but if the host is not in the way and has let go well enough, the body is just there for you to take it. The physical body shall become your body, so ignoring your imaginary body and its senses might help you get in control. Majority of tulpas already have forms, so you might be able to use that to aid you in getting to the correct mindset. Symbolism still can be a good tool, if that works well for you. Sharing the senses of your host as they are in control of the body normally might help you getting used to the physical body's feelings and make it feel more like something that also belongs to you, something you can move as well, just like your host does every day. Keep at it, even if the body feels unresponsive and heavy. Talk with your host as they can provide feedback and see if you can make use of muscle memory.
Practice, willpower and determination. That's all you need.
Switching
Mastering possession plays a key role in finding a nice and simple way of getting a switch going. While some tulpas say they can control and feel the body better while switched, in the end, if the tulpa has become very good at full-body possession and the host is very good at letting go even if they are still observing, there probably isn't going to be any change for the tulpa. The tulpa doesn't need to do anything else here to aid in switching, either, unless they have a great idea that will help the host. Switching is a skill the host has to learn, but once they've gotten comfortable enough with not being the one controlling the body, it's not as big of a step as some might think. Letting go of body control in the first place required them to find a way to "disconnect" themselves from the physical body already, now they just need to find a way to "disconnect" themselves from all of the body's physical senses. Some dulling of those senses most likely already has happened as the host and tulpa have practiced switching, so it's just a matter of ignoring the physical senses completely and taking on imaginary ones. It again is all in your mind and all it takes is willpower.
Don't rush it and get someone hurt. You, the host, want to make sure the tulpa can use the body well before even thinking about switching. Anything less is going to be pretty irresponsible.
Also made this HIGH QUALITY picture of my old MS Paint doodle, maybe it'll show some of my thoughts better in image form.
Nothing else really, thoughts, comments, something. Give me your best stuff.
edit: help i accidentally words also the image host decided to go down so pic was reuploaded