Making a Campaign World

Put as much or little as you want into it and the players will shape it with you as y'all play. 

Start with a world map or don't, just make a few points of light in an undiscovered blank world, or somewhere in-between.

There are a lot of cool generators online and good pages and groups for getting ideas.

Play with the generators over at Chaotic Shiny if you need some ideas

AutoREALM is a free map making program and is easy to use. If you're not an artist try starting with that.

Afterwards if you're feeling lucky mess around with GIMP or Inkscape with your AutoREALM map and spice it up or make a new one.

Templates to make the critters and people of the campaign uniquely yours.

Sample Encounter Tables

Religion

If you have a creation myth that might be a place to start.

Start with gods for the civilizations the campaign is set in and whatever cool stories you are using. Characters that have ranks in Knowledge (religion) will know that there are other gods of other civilizations, including forgotten ancient ones whose worshipers are long gone.

If you have players that make a cleric and pick two random domains instead of one of your gods ask them to describe their god. And whatever they come up with could be a lesser god from the distant <insert random compass direction>. I've ended up with some bizarre ones that way, a beaver god of creation, a dead crow god of travel.

The ones you come up with are the lesser gods and others, unnamed at the start, be greater gods or vice versa.

Perhaps their status fluctuates from lesser to greater to demi-god based on the number of worshipers or sacrifices.

Maybe its some of each.

Cities and Towns and places

Random Towns and Cities

And a few tables of different things to kick start my head when making places.

Roll up a couple and see what you come up with.

Rivers, Deserts and Demi-Gods

Along the great rivers that run through the deserts are nine city-states, each with its own demi-god.

Each city-states gods strength waxes and wanes with the number of worshipers. 

Their power also is tied to the city, with each mile outside the walls making the god weaker and weaker until they are mortal.

In addition to the flat roofed, mud brick houses there are five story temples in the center of every district dedicated to the city's god where farmers bring their tribute of grain and priests turn it into beer.

Below the grain silo temple/breweries are taverns and below each tavern are cool rooms for the beer. 

Within each tavern there will be always be a band of grave robbers and mercenaries for hire, they only work in other cities since their primary patron is their city's governing deity. 

Brigands, cutthroats, exiles, whatever their past, one demi-gods enemy is another's ally.

Commoners are thrown in the river when they die and feed the ever present crocodiles. The wealthy maintain ornate family crypts and bury all the deceased will need in the afterlife within. 

Only those buried within the city's walls enjoy the afterlife.

Among the commoners cultists of the crocodile god are common, when discovered they are fed to one of his many children.

The river and surrounding marshes are home to dire crocodiles, giant frogs and poisonous snakes. 

In the arid plains are giant flightless carnivorous birds that prey upon the herds of small antelopes and any foolish enough to travel there.

The endless sand dunes hide the oasis necropolises of ancient priest-kings of Set who ruled before the time of the demi-gods.

Rainforest

Mile high trees where the light of day never reaches the black water below. Each of the five layers: the overstory, the canopy, the understory, the shrub layer, and the flooded forest floor are home to different races.

The overstory is the hunting ground for all manner of flying predators. It is also home to tiny ravenous fey creatures that after a few years form cocoons and emerge with brightly colored wings. They change from chaotic evil to chaotic good with no memories of what or who they ate when they get their wings.

In the upper half of the canopy dwell tribes of primitive humans, not dumb, just tech challenged due to the lack of metal. Verdant Bloodline Sorcerers are very common.

In the lower half of the canopy there are psionic Elf-like plant creatures that grow like peas in a pod from a two mile long tangle of 10' diameter vine. Those "born" in the same pod are considered sisters, those from the same vine are a tribe. They can commune with the vine through its flowers. They all look like female elves with skin the same color as the flowers on the vine. And of course the only thing they hate more than other species are the other tribes of elves.

In the understory are the fungal orcs, spores that grow out of the dead bodies of elves. They look like white, bloated male orcs with mushrooms sprouting out of them. The bodies of other races infested with these same spores are not as hardy. Fey become shriveled and goblin-like, humans resemble rotting hobgoblin zombies.

The last glimpse of light in the shrub layer is the dismal home to a miserable race of ogres that are hosts for several creatures and diseases. Parasitic stirge-like creatures infest and control almost every adult ogre. They spend most of their adult life on an ogres back with its proboscis jammed in the ogre's head. After a month the creature looks like a discolored hump, having merged with the ogre's spine and cannot be removed without killing both creatures. The wings slowly grow larger until the creature can fly a year after the melding. This is when they begin hunting creatures at night in other levels of the rainforest.

Also at this level are the disgusting troglodyte/shrieker amalgams that expel deafening farts when frightened.

At the bottom there are endless varieties of nightmarish creatures lurking amidst the roots of the sky trees, feeding on the rotting vegetation.

A copious quantity of various oozes.

Glow Sticks (1' to 3' tall treant saplings that have been mummified by the tannic acid in the black water, and are covered in phosphorescent fungus) wander up from here at night.

Marsh/Swamp

Dinosaurs and tribes of various humanoids dominated by warring families of black dragons, chiefs and half-dragons. 

Boggards, Bullywugs, Lizardfolk, Saurians, etc.

Exploding toads, giant leeches, a dozen kinds of plants with pollen poisonous to non-reptiles, lots of poisonous snakes. 

Giant awakened constrictors with bad attitudes and the snakemen that made them that way often hunt in the rainforests.

.

And a random thought table (roll 1d20)

Below are some ideas and a map or two.

1 Blues mind seeded minotaurs and established a city-state and eventually an empire of goblin merchants, half-ogre slave soldiers, subjugated orc tribes. Ogres are used as mounts and beasts of burden.

2 Romanesque hobgoblins ruled by a dragon emperor, half-dragon senators and half-dragon centurions.

3 Shadow dragon shoguns, ogre magi daimyos, hobgoblin samurai, human ninjas and pirates.

4 Grey elf eldritch knights riding giant eagles.

5 Human picto-celt warrior society, fighter kings, surrounded by fey wood elves, forest gnomes, duergar.

6 Formorian kings, half ogre champions, half-orc reavers, mongrelmen peasants

7 Dwarf king, dwarf and human guildmasters, dwarf and human craftsmen allied with hobgoblin corsairs, hadozee sailors.

8 Dwarf necromancer queen, subjugated humans, frost giant raiders.

9 Necromancer Kings.

10 Death Moon Barbarians.

11 Gor-like city-states that raid and trade with each other. The elite warriors ride dire eagles.

12 Two races of escaped slaves from a mind flayer dominated world, Dran (a race of human/drow/goblins), and the Gorg (a mix of goblinoid races and ogre).

13 A fey race of elves corrupted by the far realm, start life as shark-toothed petals, then form a cocoon.

14 12 Tribes of orcs dominated by warring demon princes, the last humans live in a ruined city in a great swamp ruled by succubus twins, sorcerers are common.

15 Sentient female giant spiders, small normal intelligence males and a subjugated insectile goblin tribe. Select female goblins swell up to ogre size and burst into swarms of tiny spiders.

16 Followers of the god of elven werewolves and vengeance dominate a continent of ancient trees dotted with ruins of the other races.

17 Cthulhu-Punk the Masquerade city.

18 Gorthal - A sprawling mega-city of arcane slavers that exists on several worlds. Raiding parties of half-ogre slave soldiers in ornate half-plate led by wizards.

19 In the north the neanderthals are psionic and dire predators are prolific. Sapient, black-furred smilodons and winged elves live in the equatorial jungles. Nomadic clans of raptor shamans follow vast herds across the warm plains.

20 Sailing the Seven Sands, 7 different deserts dominate this world (each loosely based on a different desert campaign setting, i.e. Al Quadim, Dark Sun, Sandstorm, Necropolis, Mesopotamia, etc)