The answer is not so much a specific list of steps (task-list) but more Cosimo's political maneuvering, with family and friends, that propelled him leadership in the Republic of Florence.
His political ability resulted in real political power, which propelled their name into history. What he actually did, in most observations, is not explicitly stated -- it was more how he thought (his approach) -- that made it work for the Medici family.
On political ability, p. 1262:
On the surface, it seems obvious that Cosimo de' Medici (1389-1464) did it all. Cosimo de' Medici was multiply embedded in complicated and sprawling Florentine marriage, economic, and patronage elite networks. And he was riding herd on vast macropolitical and macroeconomic forces far beyond his control. Yet he founded a dynasty that dominated Florence for three centuries. He consolidated a Europe-wide banking network that helped induce both international trade and state making elsewhere. And he oversaw and sponsored the Florentine intellectual and artistic efflorescence that we now call "the Renaissance".
On political power, p.1262:
Contemporaries deeply appreciated Cosimo's power. Foreign princes after 1434 flocked to Cosimo's private palazzo to work out international relations, much to the consternation of bypassed Florentine officials. Cosimo was legally enshrined on his death as the father of his country-no mean recognition from citizens as cynical and suspicious as the Florentines.
On thought process (approach), p. 1263:
We use the term "robust action" to refer to Cosimo's style of control. The key to understanding Cosimo's sphinxlike character, and the judge/ boss contradiction thereby, we argue, is multivocality-the fact that single actions can be interpreted coherently from multiple perspectives simultaneously, the fact that single actions can be moves in many games at once, and the fact that public and private motivations cannot be parsed ... Moreover, especially after 1434, all action by Cosimo (never explained or rationalized) appeared extraordinarily reactive in character. Everything was done in response to a flow of requests that, somehow or other, "just so happened" to serve Cosimo's extremely multiple interests.
On Cosimo's style, p. 1263, fn.8:
Contemporaneous reports of Cosimo's personal style are as fo!lows: "He acted privately with the greatest discretion in order to saieguard himself, and whenever he sought to attain an object he contrived to let it appear that the matter had been set in motion by someone other than himself. . He replies were brief and sometimes obscure, so that they might be made to bear a double sense" (Vespasiano [ca. 149S] 196.3, p. 223). "In 14.32, just before his exile and triumphant return, a political opponent, Francesco Filefo, described in a letter how Cosimo, in contrast to his 'open and lighthearted' brother, Lorenzo, 'is, I notice, despite appearing devoted to me, the kind of man who feigns and dissembles everything. He is so taciturn that he can scarcely be understood even by his intimates and servants in his family circle' " (Brown 1992, p. 106).
Source: Padgett, John F; Ansell, Christopher K, 'Robust action and the rise of the Medici, 1400-1434', The American Journal of Sociology; May 1993.