I first began practicing yoga in the ashtanga style of Patthabi Jois and a number of triangle postures, even a subroutine (prasarita), begin that style of practice. Ashtanga starts with a number of Suryanamaskaras (sun salutations), the second type of which includes a nod to virabhadrasana, after a forward bend, the next nine postures are triangle asana.
Ashtanga can be quite an extreme practice and I tend to credit the fact that I didn't receive an injuries with the practice of the standing sequence, considering it to be warm up and preparation, "triangle keeps your safe". This is a blessing but also a bit of a curse. I find it hard to consider a practice without including some triangle asana but I've also tended to think of the triangle postures as merely warm up, preparation for the more challenging postures to come.
So when practicing Vinyasa Krama I include a number of Triangle postures directly after the tadasana sequence, sometimes with a couple of suryanamaskara sandwiched in between. As a rule I'll follow the order of triangle postures I'm familiar with from ashtanga, utthita trikonasana including the reverse twist but at utthita parsvakonasana i'll include the vinyasa Krama subroutine ( day 12) with the palms coming together and the one leg squat. I'll do the prasaritta subroutine next and then throw in the parsva konasana posture before moving on to some On one leg postures.
One thing to come out of this review of trikonasana subroutines is that I'll be spending more time in my practice on the parsva konasana subroutine (day 13) rather than just the key posture.
Another problem with seeing the triangle postures as merely warm up/preparation postures is that we can forget what an intense hamstring stretch is involved. In Ashtanga we would have practiced eight to ten sun salutations before moving onto trikonasana, the body and legs in particular are warm and well stretched out. In Vinyasa Krama we tend not to include as many Sun salutations and for this reason need to approach the triangle postures with caution.
The utkatasana and ardho utkatasana subroutines from the On your feet sequence can be good preparation for the one leg squats in triangle and the Uttanasana, forward bend, On your feet subroutine can warm up the hamstrings for the intense stretch they'll receive in Utthita parsvakonasana.
Vinyasa krama subroutines often tend to include a gentle approach to the postures, we might enter and exit on the breath a few times, going a little deeper into the posture each time before settling into the full expression of the pose. We should think carefully before dropping that gentle introduction.
NB: These are practice notes that will be tidied up and put into the new edition of my Vinyasa Yoga Practice Book along with the current sequences and subroutines. The book can be freely downloadedHERE. There is a page on Facebook HERE with all the latest sheets and updates. This book is in no way a substitute for Ramaswami's Complete Book of Vinyasa Yoga.