If you are basing your novel in any way on the traditional three-act structure, I think there are certain things you should think about when writing your first act. This applies to stories where the protagonist is goal-oriented and must work against some sort of active antagonist; other types of stories will require other types of structures, I'm sure.
In many of the unpublished mss I'm privileged to read, the first act isn't very strong. The ideas are there, the conflict is there, but there's just not enough of it. I don't like to hand out formulas or recipes for writing, but I do think that writers should have tools they can use (and no, I'm not prepared to distinguish between "formulas" and "tools" today), so I offer up these thoughts.
1. Your first act should end with the literary equivalent of a train wreck. What I mean by that is that you should be moving constantly toward a collision of conflicting needs and desires that results in the protagonist having to make a major life decision and consequently act upon that decision.
2. Your protagonist should have a clearly-defined goal. Often this is a wrong-headed goal based on a misunderstanding the protagonist has about the world. The train wreck at the end of the first act will leave the protagonist with a better picture of reality and possibly a new or modified goal to which he must direct his life and actions.
3. Your antagonist should have a clearly-defined goal. This isn't necessarily something Evil, but it has to set your antagonist and your protagonist on intersecting paths that will result in the above-mentioned train wreck. Generally, the train wreck leaves your antagonist stronger, and his goals won't change at all; he'll just keep moving in the direction of his goals and continue acting upon his desires and needs.
4. Your support characters should have clearly-defined goals. These are usually goals that are supported by or aligned loosely with the protagonist or the antagonist. Know which is which. Your protagonist could be allied with people who are actually working against his goals, even if not deliberately or with Evil Intent. Their lives will also be affected by the train wreck in some way. Some of them will change their goals, others won't, but all of them will continue to act to achieve their goals.
5. The story must MOVE toward the train wreck, and things have to REMAIN IN ACTION. Think of your first act as the opening of a game of chess, where each side is closing in on the other, and pieces are constantly being moved forward, some pieces captured and removed from the game as it progresses. Often the protagonist won't even know that there is another player opposite him, killing his pawns and planning to put his king in checkmate. The point is, the characters are all active and constantly moving forward.
You are, in a traditional first act of a traditional three-act structure, moving toward a point where all of these conflicting courses crash into each other with a big bang, from which the rest of the story will spin away toward the climax.
Your job is therefore to:
Keep your characters moving toward goals
Let your readers know what these goals are
Let your readers see what the conflicts are
Let your readers know what is at stake for each character
Let your reader see the train wreck coming before your protagonist sees it
Make sure all the motivations are plausible and clear
I do find myself thinking in terms of either a train wreck between locomotives racing toward each other on the same track, or a street intersection with two or more cars all speeding to a messy crash. Don't get me wrong; the pace of the story does not have to be breakneck. But you do need to set forces in opposition and have them collide.
The most effective way to do this is not, surprisingly, through plot but through character. What happens to people is not nearly as interesting as what people are trying to do. This is a very important distinction. Don't let your plot push the protagonist; have the plot result from the protagonist pushing against life. Agents, editors and, yes, readers generally aren't interested in characters who are reactive, who get pushed around by life. You might think that this sort of victimhood will make your characters sympathetic, and you may be right, but you will probably be wrong if you think that will make them compelling to readers. So think of the train wreck you'll be creating as a collision of characters and goals, not as the meeting up of plot strands, okay?
Sorry about all the italics. I got carried away.
Note: I am currently on vacation, so I won't be able to reply to any comments on this post. Hopefully Michelle and Davin can pick up the slack for me. Apologies all around. Also: someone needs to remind me at some point that I want to write about beginnings of stories, Chekhov's gun and how the two can work together to give a writer story options.