There were usually a number of candidates for the consulship at least. Of those usually only three or four were considered serious rivals. Catiline ran against five other men for the consulship of 63, but only Gaius Antonius and Cicero were thought to have much of a chance besides Catiline, who ended up losing to both of them. In the elections for the consulship of 59 Caesar ran against Bibulus and Lucceius, neither of whom was thought to be a serious threat to him--Lucceius had agreed to work with Caesar and Bibulus, as Caesar's colleague for the aedileship, had been totally overshadowed

Before a man could officially become a candidatus (literally a "whitened guy," because candidates for office customarily wore all white) he had to formally enter the city and present before the corresponding magistrate (depending on what office he intended to run for) his professio. The professio had to be submitted at least one trinundinum, or three market market days (held every eight days), in advance of the election, although usually it was submitted well in advance. Until Pompey in 52 passed a bill making personal submission of a professio a legal requirement to candidacy, a move clearly intended to attack Caesar individually, candidates don't appear to have actually legally needed to submit their proffesiones in person. In 63 in the de lege agraria Cicero points out that the clause in the Rullan bill preventing individuals not present in the city (he means Pompey, who was in the east still) from candidacy for the proposed decemvirate had no legal precedent, and that legally speaking there was no actual reason why even annual magistrates (like the consuls) had to submit professiones in person. Indeed, Livy specifically says that Fulvius Flaccus was elected to the consulship while sitting outside the city waiting for a triumph. The requirement of personal submission of professio seems to have been a custom rather than a legal requirement, at least until Caesar tried to run in absentia after returning from Gaul. It was an expected custom, though, since Caesar felt compelled to give up his Spanish triumph after Cato's insistence that he submit his professio in person, and Catiline was prevented from submitting his, and thus did not run, in 66 by his trial for repetundae

Campaigns for the consulship could take months, or even a year, with preparations usually going back as far as a candidate's entry into politics, since so much relied on the personal connections and reputation the candidate had forged during his career. The Commentariolum Petitionis advocates for lengthy periods of meetings with just about every important leader in the city, and while campaigns sometimes were announced at the last minute generally lengthy periods of electioneering were the norm. Campaigns were also, without exception, extremely expensive. Even the Commentariolum Petitionis has to admit that bribery is the rule, rather than the exception, and while enormous gifts were not necessarily standard voting centuries and other associations, along with a candidate's body of clients, would expect a certain amount of compensation of some kind, if for no other reason than to seal the deal, so to speak. A clean candidate would see months of continuous campaigning, which would be necessarily very expensive as he did favors and lent support for various people and groups, all paid from his own pocket. A corrupt election could be prohibitively expensive for an individual, and in the election for 59 we see Cato trying to stop Caesar from getting Lucceius elected as his colleague by putting together a coalition to shell out enormous bribes