Creation and backstory guidelines for ANY character

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Ideally a characters dots and other traits on their character sheet should reflect the character's background and visa versa.

The two basic questions every character background should answer

Player characters are a cut above most NPCs. They are stronger, smarter, more trained, and all around more capable than the average person. They are nearly always much stronger willed.
The first question you must answer is why and how is your character so skilled?
Most people, even extraordinary people, tend to settle down in one place and seek some level of comfort and stability. A badass warrior could become a wandering adventurer but more likely he will parley his skills to serve a noble lord or lady as a knight or elite guard or something similar, and in the process gain stability, land, wealth, and status. As a bonus, most knights don't have to face life threatening peril as often as most adventurers are prone to do
Most player characters travel around constantly seeking adventure for either selfless or selfish reasons.
The second question you must answer is why is your character adventuring in faraway lands instead of trying to put down roots somewhere?
These two questions can easily be linked, the same thing that drove your character to become powerful also drives your character to go adventuring.

Short campaigns versus longer campaigns

A short term campaign doesn't need a complicated backstory. Hypothetically if you are running a short term campaign over 1 to 4 sessions with the following premise:
"a group of orcs has been routinely extorting tribute from a group of human villagers every year. But this year the tribute demands are so high the villagers will not survive the winter if they pay it, so they asked adventurers for help."
You don't explain why your character took up the life of an adventurer, you just need to explain why your character is taking up this adventure, right now.
A character background of "My dwarf character really hates orcs and is mildly sympathetic to humans, so he volunteered when he heard of the villager's situation" is acceptable.
"My theurgist believes in protecting the weak, so she volunteered when she heard of the villager's situation." is acceptable.
"My character's uncle and cousins lives in the village, so he volunteered when he heard of the villager's situation" is acceptable.
Even "My character likes to kill people and doesn't want to be arrested for murder, so he volunteered when he heard of the villager's situation." is accepable.
Usually campaigns are intended to last longer than a single story arc, in which case it's a good idea to come up with a meatier background, though it is possible to overdue it while writing a backstory. It can be anticlimatic and disappointing if your character's past is far more exciting than your character's present and future.

The Meta reasons behind character backgrounds

Part of the reason we come up with elaborate character backstories is because it's fun to write and tell stories. Part of the reason we come up with backstories is for logical consistency relating to answering the two questions for why your character is so special.
But in an RPG campaign, the main meta reason for writing a detailed backstory for your character is for storyhooks. Your character's past creates a web of contacts, friends, family, enemies, and mentors that can all drive interesting stories. A lot of characters fit the mold of tragic orphans. It is debateable whether this is a "classic" or a "cliché" but remember tropes are not always bad thing and it is not a problem if your character's backstory closely follows a well known fictional or real world historical character or a well known literary archetype.
While an RPG campaign probably has a main metaplot such as country A is invading country B, an evil dragon is nearing the completion of a centuries long scheme, or some other big event, character backstories provide interesting sideplots and if a character backstory side plots are interwoven with the main metaplot, so much the better.
Good backstories make it easier for the Game Master to write stories. It also makes it easier for players to get invested in the campaign and to use an actor adage "What is my motivation?" to help inform roleplaying.

Into the Weeds

Macro Photography of Green Grass by icon0.com

Every character has or at least had a family, since even orphans had to come from somewhere. You should pay at least cursory attention to how and to whom your character was born. This is going to influence your character's early education and his moral outlook and ambitions.
While it is certainly possible your character has a tragic backstory as an orphan or exile or a Cinderella fleeing an abusive family, there are some adventurers that still have a good relationship with their family. Most Scarterran cultures, both peasants and princes alike value primogeniture. The first born (or the first born male) inherits the family's farm, the family's shop, or if a noble, the family's land and title. If the extra children want to stand out, they may try to carve out a new life in the army, a mercenary group, a troupe of traveling performers, or a priesthood. In other words, they become adventurers.

Not counting characters literally or figuratively raised by wolves, every character has a homeland and native culture. Maybe your characters fit in well with his or her home culture or maybe they were rebels and misfits. Most people like some aspects of their homeland and dislike others. This is worth thinking about.
Some adventurers that are fiercely loyal to their home cultures and go forth into the wider world to spread their culture's ideals or advance their homeland's interests. Other characters who become adventurers have a complicated relationship with their home culture, and they became an adventurer so they can figuratively or literally put their past culture behind them.

Player characters are exceptional people. Some are born exceptional with unusual birthrights. Most have some form of a formal or informal education or they were forged by fire through by enduring hard life experiences. Probably some combination of all three of these things. The specific combination of these factors will influence how your characters sees herself and how she sees the world at large.

To flesh out your character's backstory, pay careful attention to Merits and Flaws lists. If you aren't playing a one-shot adventure, you should probably spend more time considering Merits and Flaws than you spend filling in dots on your character sheet. If you have an idea for a Merit or Flaw that isn't on the list, most Game Masters are happy to negotiate new ones.
Flaws provide extra freebie points and Merits provide useful things, but beyond the concrete metagaming advantages, Merits and Flaws can eaisly provide story hooks and they can provide depth and nuance ot your character's personality, moral outlook, and short-term and long-term goals.
Example, Robin Hood is a charismatic leader and a world class archer but the meat of what makes him an interesting character is in his Merits and Flaws, not his abilities. He has the Noble Merit, Agent of the Crown Merit (via King Richard), Folk Hero Merit, and has the Outlaw (via Prince John) and Out of Favor Noble Flaws among other potential Merits and Flaws.

Alignment and Religion

Scarterra and Scarterra D10 uses the same basic nine alignments familiar to most D&D veterans but these are guidelines, not hard limits. In place of Good, Evil, Neutrality, Law and Chaos, Scarterra has good, evil, neutrality, law and chaos. These values are present among all free willed beings, but they are not metaphysical forces. You don't even have to pick an alignment for your character at all if you don't want to though you should probably put some description in what your character's goals and values are even if they don't fit under one of the 9 classical grid boxes.
Scarterra doesn't have demons, angels, devils and acting as living avatars of moral outlooks, but they do have spirits affiliated with the Nine that vaguely fill the same niche.
Speaking of the Nine, it is probably a good idea to figure out your character's relationship with them. Scarterra does not have any atheists or agnostics as we understand these people today, but Scarterra does have more than its fair share of impious mortals.
Some believe the Nine are not deserving of worship because they believe the Nine are uncaring assholes. Some simply don't bother worshiping the Nine because they perceive little to no material benefit in it. Some who worship purely for public appearance, and a great many worship the Nine out of blatant self interest rather than out of true devotion.

Alternatively, if you want to play a moderately pious or a very pious character, you have a lot of character options. Remember that not all pious Scarterrans are theurgists. It's rare, but it is possible to play a theurgist with wavering piety.
Not all priests are theurgists and not all theurgists are priests. The same goes for the various holy orders and other groups your character may be allied with or opposed to via your character backstory and Merits and Flaws.

Symbol of the Nine (with artist's permission) by Pendrake

Sub sections by character archetype

So you want to play a warrior?
So you want to play a mage?
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So you want to play a rogue/expert?