Good idea. Here's a few paragraphs about the setting:

This RP takes place in a forested realm with mountains, valleys and caves. Think of it a bit like iron age Gaul, or pre-Roman Western Europe. It is not based on any goblin-related media, such as the webcomic "Goblins" or anything from Dungeons and Dragons. That said, some common tropes exist in this RP and those, such as goblins being primitive and tribal. These goblins villages are very simple, being made of wood, straw, and sometimes, a bit of stone. Think thatched huts and the like. Most goblins live as farmers, fishers, hunters, and other similar occupations. All adult males are expected to fight when the situation calls for it, but there are a few full-time warriors, usually the personal guards of a chief. Females can fight too, but aren't expected to under most circumstances. 

The goblins look much like the standard fantasy goblins: green skin, "elven" ears, humanoid in their general shape but much smaller than a person. As for their clothing and equipment, it varies, but something like pants, shirts, loincloths, even shoes (which are rare in depictions of goblins) are around. You can dress them more or less as you wish. These goblins don't have much hair, but females might have more, if only to help distinguish them from the males. You have considerable leeway in that regard. For combat purposes, the goblins can fight with any number of weapons, but I'd suggest the use of spears, short swords, short bows, daggers, slings, maybe even small javelins. The goblins are not illiterate, but their writing system is crude and literacy is limited to a few shamans and others. Even the chiefs are mostly unable to read. 

As for their culture, the goblins live in villages. Each village contains one tribe. Further, each tribe is part of a series of related tribes called a clan. Clans are sometimes united under a figure of a king, but this only happens when the tribes need to unite to fight a larger, common enemy. All of the tribes of a region are very rarely united under a single ruler of all the goblins (or at least, most of them, as there will always be a few dissenting tribes). This figure is called the high king, and his leadership usually lasts for the duration of a serious threat. When peace is restored, the many clans want to got their own way. While they would continue to nominally recognize the high king as their reigning lord, they would rule themselves in practice. 

Rulership among the goblins is hereditary at the tribe level, elective at the higher ones. If a chief dies with no heir, a new one is appointed by the religious authorities. Speaking of which, the goblins have many little cults and worship many gods. These religious practices differ greatly between clans and villages, and their religion is clearly influenced by their geography. A fishing village would be much more likely to follow a water cult than a village dependent on farming grain, which would probably revere a fertility god. When a chief or important shaman or warrior dies, he is buried in a mound along with his possessions. This could include things like weapons, jewelry, and even mundane items such as pottery or tools. 

As for gender relations, lets just say they treat females as well as males in many tribes, and that it varies in others. I suppose it is best to treat them the same, although I'm not going to force players to play it either way. On a final note (as if this wasn't meandering enough!), there are several migratory tribes and clans, including some tribes which travel unattached to any clan. These tend to be disruptive if they attack a weaker, sedentary neighbor. On the whole, sedentary tribes tend to be more powerful than their migratory neighbors, except for periods of war between settled tribes, periods of famine and/or plague, or if a large number of migratory tribes gangs up on a smaller number of settled people. 

Is that good? Should I add anything more?