Characters.  They're one of "The Big 5" (story essentials).  Characters are a must, but readers prefer to spend their hallowed reading time with good ones.  So...what makes a good character?  Is it their looks?  What they say?  What they do?  How they feel?  Answer: Yes, yes, yes and yes. 

...BUT...

The difference between a good character and a flat character is this: Good characters make the reader feel something.  You can't wait to meet up with the girl in the red dress again because you like her.  You can't wait for the sweaty loudmouth guy to go away...far away...because (wait for it)...you hate him.  Probably because he's mean to the girl in the red dress.  Maybe you think a character is secretly evil, or a superhero in hiding, and while you're not entirely sure yet, you'll be keeping a close eye on him.  Love, hate, curiosity...all great feelings to arouse in your reader.    

So when you create a character, don't just focus on his/her looks (lame, lame, lame).  Think about the reaction you want your reader to get from said character.  Once you settle that score, creating the dialogue, facial expressions, clothing choices (not to mention personal choices), and so on is a piece of cake!  And fun!  When your readers connect with the characters, they keep reading.  Remember, if they're not feeling it, they're forgetting it.