I like to be able to build characters for a tabletop roleplaying game quickly. A fast build is useful for a player when you're planning a short one-shot session and don't want to spend half of that session on character generation. It's useful for a Game Master when you're trying to generate several characters for a games convention or a sudden RPG emergency session.
I've migrated permanently away from Wizards of the Coast's D&D, and for 5e style game play I've adopted Tales of the Valiant. I've gotten the Tales of the Valiant character build process down to just under 12 minutes.
The theory behind the 12-minute build is that much of the power scaling in 5e is attributable to the proficiency bonus, and that the primary mechanic in a quick game is the d20 roll. Sure, each class has special features that get introduced along the way to help characters gain power, but in a one-shot game those features are secondary to the real workhorse of 5e: rolling a d20 and adding your attribute modifier and proficiency bonus.
Pick a class, and turn to that page in the rulebook. Flip through the class until you find the Quick Build sidebar. The first item in this list are the key attributes for the class. Prioritizing those two attributes, use the ToV standard array of 16, 14, 14, 13, 10, 8 to assign values and modifiers to the six attributes.
Write down the features listed under Class Features, including Hit Points (use the average), Saves, and Equipment.
In some cases, specific equipment isn't provided, and instead just a type of armour or weapon is listed (simple weapon, martial weapon, and so on). If you know your DnD weapons, you can write in a specific weapon, but if you don't then just make note of the type, and fill in the specifics later. Personally, with weapons and armour, I often let the player choose before the first combat begins.
Other standard values at 1st level:
Pick 4 Skill proficiencies (2 standard, plus 2 as a custom heritage.)
Don't bother selecting a heritage or a background, you don't have time for it. Players can let a heritage and background emerge as they play. You can either formalize what emerges with custom bonuses later, or just use it as a prompt during roleplay ("Hey, remember I supposed that I grew up in the slums during that first session? Can I get a bonus to avoid losing gold to that pickpocket?")
Choose a lineage, and write down all inherited special traits (elves meditate instead of sleep, kobolds tinker, and so on).
I find Talents really fun, so I do take the extra time to jot down the bonuses afforded by a Talent. There's a Talent suggested in the Quick Build sidebar, so just look that up and add the corresponding features to the character sheet.
Spells are really well organized in Tales of the Valiant, thanks to the various Sources of magic. If you're building a spellcaster, look at the paragraph describing their spellcasting ability for what Source of magic they use: Divine, Arcane, Wyrd, or Primordial. Then turn to page 246 and pick a out as many Cantrips and 1st Circle spells afforded to your class.
Standard values for the spell sheet:
If you had to use placeholders for weapons, turn to page 136 to get the stats for armour and page 138 for weapons. Write the stats in the Attacks and Armor sections of your character sheet.
Give yourself this much coin:
Write down everything listed in a Dungeoneer's Pack (page 142),
It's not perfect, but it's only 12 minutes. There's plenty of room for experienced players who are familiar with their class to choose a heritage and background, or to take advantage of some class feature that I skip over. You can make an allowance for a new player to leaf through the Player's Guide (or Deep Magic, also by Kobold Press) for an interesting spell while another player is taking their turn in combat. The idea, though, is to get everyone at the table a playable character in the minimum amount of time, and for that playable character to feel like a fantasy RPG character.
Don't over think it, don't sweat the build. As usual, game play will solve everything.