Including NPCs in a game seems easy: you just slap a name on a stat block and you're done. This is Gobgor the goblin, who fights the heroes. This is Shopkor the shopkeeper, who sells stuff to the heroes.

I'm not going to get into naming NPCs well; I'm actually not very good at it. But there are easy steps to make any NPC evocative and useful at the table. This is particularly important when you're writing adventures, because the NPCs need to be simple (because some GMs and players will blithely defeat or ignore them) but have compelling points (because some GMs and players will want to flesh them out far more than your text provides). You don't really want to use more than a paragraph, but you don't want to use much less than that, either. 

A good way to strike this balance is to write these six sentences for each NPC.

* An interesting and applicable background note. You don't normally need a really long or convoluted background except for the most significant campaign-defining NPCs. ("Gobgor was among the largest goblins in his warren growing up, which quickly showed him that he could bully others to get what he wanted." "Shopkor was the eldest daughter of a wealthy merchant who learned the art of negotiation at her father's side.")
* A relation with one (or more!) other NPCs that the heroes are likely to encounter, or have already encountered. ("Gobgor is the undisputed leader of Goblin Castle and the spellcaster Gobwiz idolizes him." "Shopkor resents the fact that Mayor Jailsem jailed her father for trumped-up charges.")
* An immediate goal, preferably one that impacts the heroes. ("Gobgor knows that he needs to drive the heroes out of Goblin Castle or he'll lose standing." "Shopkor is more interested in obtaining influential allies, such as the heroes, than in turning a profit, so she sells to them at a discount.")
* A long-range goal, preferably one that the immediate goal advances. This goal might be on a longer timeline than the interaction with the heroes, be something the heroes prevent entirely, or be something that impacts the heroes at a later date. ("Gobgor hopes to someday rally sufficient goblins to his banner that he can lead them against the town of Bountyfarms to take it over." "Shopkor plans to silently back anyone who seems likely topple the corrupt Mayor Jailsem, so she can take over as mayor of Bountyfarms herself.")
* A personality quirk that the GM can use at the table. ("Gobgor likes to shout 'for the goblins of Goblin Castle!' in battle, casting meaningful looks at other goblins so they know he's fighting on their behalf." "Shopkor often refers to her father during negotiations with phrases like, 'now, my father would charge you ten gold for this, but I'm willing to sell it to you for eight.'")
* A physical appearance the GM can use to describe the NPCs. ("Gobgor is immense by goblin standards, nearly as tall and as wide as a dwarf, and has a shockingly toothy mouth." "Shopkor has a haggard, troubled appearance despite her notably fine clothes, but she has a ready smile for anyone with whom she's dealt in the past.")

Once you have these six bare facts, you'll want to weave them into a cohesive narrative so your paragraph reads well, but this is a good start to providing a fleshed-out NPC.