Conference season traditionally gives each of the main parties a week of owning the news and, they hope, a poll boost. They are also the time when leaders with something still to prove are expected to show they mean business. A bad conference can damage both credibility and popularity.
Gordon Brown had several "make or break" conferences, according to the commentariat anyway. It didn't make any difference. His first as leader saw him hint at a snap election, only to back down and to gain him the unwanted reputation as a "ditherer". He was unable to shift that tag.
Ed Miliband will enter his first conference as leader level in the polls with the Tories, or with a small lead, depending on which one you read. Your interpretation also flavours the results. Miliband's approval ratings might have gone down recently, but he is still the least unpopular between himself, Clegg and Cameron. His personal ratings are also similar to those Cameron received when he'd been in charge for a year.
A good speech will help his image, which has been a problem. The only way he'll really make headway in voters' minds though is through consistently saying the right thing and responding effectively to political events. He did well during the outbreak of the hacking scandal, more is needed. The political village gets excited every week at prime ministers questions, while it passes much of the country by. Conference season is little different.
Clegg's Lib Dems are failing to reap the benefit of being in coalition, with poll after poll still showing that around half of those who voted for them at the last election won't do so again. Lib Dem conference won't do anything to change that. Much as a bad conference for Miliband will lead to the same headlines being trotted out about his "poor leadership" and a good one will excite his friends and go unnoticed by most people.