To me, the easiest part of writing is composing dialogue. I simply put myself in the head of a character and yap out whatever is needed to advance the plot. The other fellow responds and a conversation is started.
There are rules. Dialogue must appear to be legitimate without slavishly copying what people actually say. No one wants to read “John, uhh, can you, uhh, pass me the sugar?” Skip unimportant stuff and avoid the strange sounds people add to their conversation.
Dialogue must never be used to advance the plot if this will compromise a character; nothing pulls a reader from a story faster than a character who speaks unnaturally. In this situation it is best to adjust the scene, alter the timing or use another character to advance the plot.
Dialogue is used to define characters, build stress, advance the plot, and to introduce humor. Readers love good dialogue. Use it whenever you can.
Your cast of characters will make or break your story. They must never vary from the characteristics that you have assigned. If Judy, the most timid of your cast, is the woman who fights off the angry tiger and saves the day – you better work hard to justify her new-found courage.
Perhaps your hero is Jack Cracker, a battle hardened veteran from Afghanistan. Trapped deep within the jungles of South America, he must guide a troupe of nuns and orphans through territory claimed by the local drug baron. He is stern, he is tough. Jack has no fault, no weakness. On his push to freedom he catches and kills many of the drug baron’s soldiers and, in the final chapter, the orphans safely reach the coast. Although everything works out well, Jack is a poor character. As described above, he attracts no empathy; readers, comparing his absolute perfection against their own inadequacies, will be rooting for the drug lord. To promote sympathy for your characters, include faults, bad habits, awkwardness… anything you can to make him appear as human as possible.
As a rule of thumb, try to avoid creating more than seven main characters in a full sized novel. As the size of your cast increases it become difficult to maintain a cohesive storyline. Also, readers will have difficulty keeping track of a large number of characters.
To avoid reader confusion it’s a good idea to ensure that the names of your characters show no similarity. If John is used, don’t use Jake. Try Frank, or better yet, Edward. If your lead character is Judy, avoid Trudy or Julie. Linda would work but a one syllable name like Anne would be best.
Many authors work hard to provide a complete physical description of their characters. This forces the reader to see the character exactly as the writer intends. While useful, this does limit the reader's use of their imagination. Take a look at my short story, Running Fast. While the main character was well described, a physical description was not provided. In this case, it was not required.
Work hard to build your characters and your story will come alive.