The approach and a few loose thoughts
Guides don't really work.
It's true. Of course, this shouldn't really stop anyone aspiring to make a headmate, but the basic finding is, at least for me who spent a few months doing this stuff regularly every day, that things don't really work for people. Instead, it's much more beneficial to use guides only as inspiration, something like a literal sign on the road, but I wouldn't recommend referring to them that much. Being open to new ideas is very good, but then again getting to know some useful knowledge is very hard.
The right approach to making tulpae would be something along the lines of "inventing" things, keeping your own journal where you write down all your findings and pay special attention to things that "worked", so that you can start off next sessions practicing with them rather than sticking to the normal forcing routine. All in all, people on IRC or on forums may tell you a thing or two but the problem is that they usually talk from their own perspective which doesn't have to relate to yours.
Forcing also shouldn't really be considered a routine since routines create boredom, a thing that absolutely detrimental to any relationship, not only these of the type tulpa vs host. Simply, you stop meeting your friends when you get bored around them. Interaction should be the aim from the very start, as Fede-Lasse mentioned in his guide on the forum. Even if tulpae are not vocal yet, it's still very good if you spend every minute of your waking time with them, especially at the early stages of creation.
The fact that tulpae are a rather subjective phenomenon makes it very hard to consider making them a science (it isn't really one). More importantly, the lack of failproof guides and a few other issues makes it so that hosts are no scientists, even if they sometimes like to be perceived as such.
The fact that the experience is subjective doesn't really stop us from establishing one thing, i.e. that tulpae are creatures that express themselves by means of memories and memory exploring is something that can be utilized to speed up the creation process. Just think about memories of people who possess their physical bodies. You remember their faces, mannerisms, tone of their voice and so on. The same applies to the ones who passed away. You still are able to recall what they were like, even if they no longer are here. Or what they would say in specific circumstances. In a way, tulpae are much like memories of dead people. Walking, talking and being themselves, but without all that flesh part.
Anyway, the creation of a tulpa usually entails creation of a set of very precise memories. Are tulpae people made up of memories? Very early, they are actually passive in their ways, only able to give opinions and so on. What makes them actual persons is the inflow of the information of their own (the things they know but the host doesn't - and didn't know before) and the ability to make changes and do whatever they wish regarding their own fate. These two aren't all things that make a personality, but hey, they are pretty much basics, right?
Now, about interaction. A while ago I said that it's much more beneficial to concentrate on interacting with tulpae rather than focusing on the quality of imposition. In fact, the more you interact with them, the better you see them, hear them and so on.
For the obvious reason of interacting with wonderland you would have to force a body of wonderland, the one of your own. Very early wonderland explorations (or rather, memory explorations) would center around memories of your own body. Let's say, you sit in a quiet place where no one can see you and you clap or rub your hands and then focus on the memory of you rubbing your hands. And then you put your hands in front of your face and remember their sight as closely as you can.
And then, when you're done with playing with your hands, you would take a mental snapshot of your room and close your eyes and remember how it looked. You'd pay attention to all the details and maybe you'd devise some techniques that work for you.
The fun part with memories is that you don't really have to be near actual things to experience it. The memory training may possibly take a few months or even years, but you can't really fail it since whenever you begin anew you don't start from point one. Experiencing memories vividly is the key (one of a few) to successful tulpaforcing. When not forcing, I usually pay attention to how I experience things - how I look at them, how does it feel like to be touching books, what their texture is like and so on.
Interacting with wonderland is an experience that is a combination of visual, physical and aural memories and frequent forcing of this kind may lead to cases of dissociation.
Here's a guide on eidetic memory I found recently.