I'm really lazy when picking up new series so what motivates me to read the first chapter is the premise. It can be anything from a Wikipedia summary or a one sentence synopsis akin to the Laconic subpage on TVTropes.
What makes me want to continue are the protagonist and the pacing of the story. Since the story will be centred on the main character, they have to be someone I can like or at least tolerate until their character development. If the characterization isn't strong at all, the manga should at least make up for it with the secondary characters or have the plot be
really interesting.
The pace is important too. I know that there's a high risk of cancellation in the early stages if one's publishing in a magazine, but the plot shouldn't move too fast nor should it move too slow. It should offer us something here and there that will keep us hooked but making sure at the same time that it doesn't offer too much.
Over in the WSj thread, FanOfAniManga wrote a
good post about what makes some new manga more successful than others.
Anyway good luck, Shabozz!