One technique - analysis.
Before you can really launch your characters into that first encounter, you have to know what they're all about. Delve into their backgrounds. Where were they born? To what kind of parents? How do they usually solve their difficulties? Do they fight or do they retreat? Do they mask their true feelings or are they perhaps too open, courting hurt?
That first encounter, while it seems simple, sets the tone of a relationship that must last throughout the novel. The way your characters react is a microcosm of everything to follow, hinting at the broad range of motives and quirks that define their personalities. This is the way they always react to each other. They will harbor the same grudges, tell the same lies, attempt thesame manipulations over and over again, each time with a different little twist, but they will behave according to the nature you have shown us at the start - until they have grown sufficiently to break out of their pattern and can take control of their lives.
That is, basically, what every novel is about. Hero and herione, acting upper inner or external pressures, learn to break out and take control of their lives, thereby finding happiness and often, too, love.
It is an accepted rule of dramatic presentation that for a story to move ahead, the characters must change and grow. Therefore, when the reader first meets your fictional people in Scene One, they must be presented with all their flaws and masks, all their rationalizations and self-delusions. That makes it tricky, for they will not always say what they really mean, nor will they be entirely honest with each other. Like real people in difficult situations, they will get at a problem obliquiely. They'll hide their true feelings. They'll rationalize, counterattack, play games. All the maneuvering for position is touched upon in the first scene. All the hidden, underlying motivations are implied by the ways the characters first appear - by their clothes, their mannerisms, their speech patterns, the way each tries to attain his own end.
Remember that in every scene somebody must want something; somebody gets something. And, of course, while the character continues with his quest, the reader is also gaining something - information.
Sometimes, when a reader first meets a character, they'll say one thing but mean another. That is the way readers understand them - by seeing how their actions are opposed to their words. It is also how readers see them change and grow - or fail to grow.
In a novel, use very few words to indicate those deep and fundamental feelings. But as the writer, you have to *know* them completely, or else those few words could never be written, and the novel would lose the impact and its depth. But most important, without this background knowledge, the characters could never have really come alive in the fullest possible dimension.
So, before you launch into a story, write other stories, sometimes dozens of them, in notebooks. Begin by giving him or her a name. Where did that name come from? Names are important, because everyone is named by the people closest to him. The name expresses the parents' expectactations. It also conjures up memories and symbolizes the family's hopes.
Names can, therefore, become an essential part of the plot, certainly part of the total metaphor.
Often the things already in a story can be exploited to greater advantage if only we will stop to think about them. It often seems that our inconscious mind has already prepared the material for us, ready to use when we dig a little deeper.
Sometimes, in an effort really to know a character before you let him appear on the "stage", question him. Ask him about his dreams, his memories, his fears. Or have him write you a letter about what he most desires or most fears in life. How can you really know a person, unless you know his strongest emotions?
Every good story is really two stories. There is the obvious external quest for a goal - to survive a danger, to succeed in a career, or to find love and self-esteem. Beyond the obvious disire lies something deeper, which we can uncover only if we know our characters well. A good book provides a bonus, not only to the reader, but to the characters as well.