This is a simple way to "kickstart" possession. Note that this is NOT intended to give you full body possession overnight, just to give you a running start. You will still need to do normal possession practice. I recommend using this as a supplement to other guides on possession or with other exercises.
First, you need a tulpa capable of independent movement.
Then, have that tulpa adopt a habit you can replicate in real life with your body, such as yawning, sighing, stretching, something simple and nonchalant so people don't give you funny looks.
Eventually the tulpa will be the one doing the actions instead of you and there you have it, possession.
Finally, refine it with other exercises and such.
Again, as with all things, this is subjective and might not work for you. If that's the case don't get discourage and feel free to tweak this to your needs.