Oi, look at that, folks are posting. Guess I'll post, too.
Just a tip I'd like to share. Er, not even much of a tip, really, but an observation. I got the idea from Methos ages ago, but the wording is my own, so as to avoid putting words in his mouth.
Both visualizing and imposing as I've encountered them have something important in common: presence precedes visuals. Even after months of not being terrible at visualization, this holds true; I feel my tulpas qua presence before I sense them by the five (whether imagined or imposed). This is the trivial part.
Here's the tip: Take presence to apply not just to the tulpa's form but to every part of their form. Instead of focusing on the five senses, on the perceptual content, it's helpful to shift one's awareness to presence alone. For example, instead of visualizing Clair's hoof, or feeling it by imagined or imposed touch, where is her hoof? Where do I feel its presence? Where is her tail? Do I feel its presence across my lap or is it hanging off the side of the bed? With greater detail, where is she looking? Can I feel her gaze on me or on something else? Are her nostrils flared in frustration? Is her head turned to the right or left? Have the hairs in her mane drifted to the right or to the left of her neck, and in what proportion? You can really go deep into detail; as deeply as you could were you doing rote visualization.
Too, as in visualization, try to hold as many of these details in your mind as you can. What's great is that you're dealing with uniform content here; you don't have to worry about holding sound and vision and touch and smell together, or about straining not to forget one while dealing with the others. That will come later, and, if my brain is not unique (and I'm 99% sure it isn't), develop on its own as you build up the habit.
So you can do this whether placing your tulpa beside you as you fap or whatever, or engaging with them in your mind, and it's a lot less stressful than worrying about all that sensory junk, which I've found can be frustrating whether one is just starting out or having a bad day as a veteran.
And I guess I should clarify in case my use of the word "presence" isn't clear: As it was best described to me in the early days, you know that feeling you get when you know or suspect someone is walking behind you, or when someone's body is hovering close to yours? The notion of their being there as it manifests psychosomaticly.
There, tip given. Maybe it'll help someone.