I was exactly where you are about 6 months ago.. Obviously others with more experience may have better insights, but I'll tell you what steps I went through as I improved (although the main step was spending hundreds of hours throwing) from throwing around 275 to now throwing 350, all from a standstill, no x step, runup, single step or anything. That's important for me, because the main thing I realized is that I had to SLOW DOWN the first 90% of the swing.
Basic starting position is standing 90degrees, shoulders in line with my trajectory.
First realization: rather than reach across my body with my throwing arm, turn hips and shoulders almost 180 degrees from target, almost facing backwards, weight slightly over rear foot, but still balanced. Front foot has heel up.
Second realization: still pulling with arm too early, so loosen muscles and grip to where I'm only using enough muscle to hold my arm in position. VERY LOOSE. Exaggerate the looseness to get a feel for letting your front foot heel drop, shifting the weight to center heading forwards simultaneously turning hips and consequently shoulders back to 90 degrees in line with your desired throwing line.
Third: I was spraying the disc all over, because I didn't know when to start pulling and pinching the grip tight, and I was pulling my head back, which made my body follow, and mostly I pulled them right (rhbh). I started keeping my head down, and making sure I SAW the disc passing very close to my chest, below the pec muscles. This was a big step. It made me pause with my hips and shoulders in line with my trajectory, and helped me learn how to load the tension as the disc passes the right pec..
Fourth: from that position, pushing with my rear foot against a bent and braced front leg, the hips open towards the target, and get out of the way, or assist the rapid shoulder opening that goes with pulling the disc from the power pocket forward. I don't actively pull with my arm until the disc is passing the right pec.
At this point I was throwing a consistent 330 from a standstill, but felt there was still something big I was missing..
Fifth: Nose down and grip timing. This is where I am now.. When I focus on keeping my wrist down in the handshake position and pinching hard, assuming all of the rest has worked, I'll get them out past 350 now on a low golf line.
This was all while reading everything I could find by Blake T, Bradley, etc, so go to the source and read for yourself and go try it out. I'm still a beginner, and don't make any claims to expertise, but thought I'd relate the developments I've been experiencing. I certainly don't intend this to be a recipie for a good throw, just what had been working for me.