I'll share with you one of my approaches to this handling NPC creation.
First step - don't roll stats. Use a standard array and assign as you like.
- Is it just a peasant quality? 11, 11, 11, 10, 10, 10
- Is it someone exceptional? 13, 12, 11, 10, 9, 8
- Is it someone elite? 15, 14, 13, 12, 10, 8
- Don't like one of the results? Arbitrarily change it.
- Need a skill role on the fly? Modify a d20 roll by 1/2 their hit die + appropriate attribute score
- Want them to greatly proficient in a skill? Make a note in their stat block for that skill is equal to their level + 3 + appropriate attribute score
- Want them to be an expert in a skill? Same as above but make it +6, assumes they burned a feat
Also the 1/2 hit die plus appropriate attribute score works great as an on the fly modifier when you don't know the modifier for any monster or challenge. Don't spend minutes looking or calculating something.
Next make a few notes about equipment you want them to have, beyond what is typical. Assign a few personality traits and other useful information. There are loads of random tables to be had online, or in your DM guides. I often refer to my treasured, old 1E DM guide for random tables to help me out when I feel stuck, or just want to mix things up.
Assign hit points based on the hit dice, Con bonus & how tough you want the NPC to be.
Give them a name. Sometimes if feels like the bane of a DMs existence is when a player, during an unimportant and routine interaction with the world wants to know, "What is the bartenders name?" Many years ago I came across a document created by some wonderful, sharing, caring individual out there (ironically, I don't know their name) which was just a list of hundreds of names. I printed it out, and keep it in the back of my DM notebook. When I use a name, I cross it out.
Done. Notice, I don't roll much (or at all) in NPC creation. Don't get me wrong, I have lots of dice and like to roll them. However, I am a busy guy and this is not the place where rolling really makes any difference. The process should only take a few minutes, and with practice you can do it on the fly when an unexpected need for an NPC arises.
If the NPC survives to become a longer term piece of your campaign, just add more notes as you go along. Make up stuff as you go along, but don't forget to add it to your stat block notes. Players love the consistency when NPCs 'remember' something about the last time they encountered them, and are put off when one day the NPC is bald and the next time they see them they have a full head of hair. Its the little things - if you describe something, write it down.
I acknowledge if you are playing a version of an RPG where character creation is a very simple process, then some of this is not pertinent for you. Other parts you might find useful. I'm always interested in hearing about your tips or tricks which improves NPC building.
The dice never lie. (but only use 'em when you need 'em)