I'd like to share a simple concept. If your protagonist sucks, your story will suck.
The engine that drives every story has three parts: a protagonist, something the protagonist wants, and an antagonist (human, environmental, psychological, etc.) who obstructs the protagonist's attainment of that goal. When you relate what the protagonist does to overcome the obstacles in his way, you are telling a story. Since so much rides on the protagonist, he'd better be interesting.
Here are a few tips for writing protagonists who engage and interest readers.
Goals: as all writers worth their salt will tell you, a protagonist must be properly motivated. There must be some goal that drives him through to the end of the story. Passive characters tossed about by events are dull.
Pseudorealism: note--not realism (unless you're writing interpretive fiction or nonfiction). For genre fiction the idea is to give your characters, especially the protagonist, enough believable personality traits to balance the make-believe elements.
Luke Skywalker is a space shaman prophesied to destroy a galactic empire. If someone approached you today and made the same claims about himself, you'd rightly doubt his sanity. However, we suspend our disbelief in Luke's case because we also see that he's a working guy lamenting his frustrated dreams. That brings us to...
Relatability: a protagonist's mindset and motivations should be largely intelligible. This doesn't mean that you have to spell everything out. In fact, a touch of mystery is good for sci-fi stories. However, if your main character is inaccessible to common human experience, readers will have trouble vicariously inserting themselves into the tale through him. That in turn leads us to...
Sympathy; not Pity: the key to engaging readers is to ease their acceptance of the protagonist as a vehicle for their own vicarious experience. They must live the story through the main character.
There is a spectrum of audience reaction to certain characters that runs from empathy to sympathy to pity.
- Empathy: feeling what someone else feels as if you were that person.
- Sympathy: commiserating with someone else's emotional state.
- Pity: sorrow for another's suffering with undertones of negative emotions like regret, disappointment, contempt, etc.
It's easier to describe what sympathetic characters aren't instead of what they are. They're not sad sacks; nor do they have to be perfect. Protagonists can even have genuinely rotten flaws such as flagrant bigotry and past murder convictions. As long as the character has at least one redeeming virtue and expresses at least tacit remorse for past wrongdoing, he can earn our sympathy.
These are just a few qualities of effective protagonists. Post any others you can think of in the comments.