I get the main ideas, that he used people against each other and built up his power, but I'm particularly interested in how he built up power within the party and used disputes with Trotsky to further his cause. For example, I found a site which cited Trotsky's criticism of bureaucratisation as a cause, but it didn't really explain why.
One key reason was that Stalin held the position of General Secretary within the party from 1922, this allowed him to control membership to the party and to place his supporters in positions of authority, steadily creating a broad support base for himself.
It even earned him the nickname 'Comrade Card-Index'.
"His main position as General Secretary was perceived as dull and essentially not useful to gain a strong political profile, earning him the nickname “comrade card index”. But in reality, the post of General Secretary allowed Stalin a different kind of power: The control of party members. Thus he was able to put his own supporters into place and establish himself a strong base for support"
Why did Stalin emerge as Leader of the Soviet Union? Christian Kliesch, (2007)