If you read the first chapter carefully, which acts as a kind of introduction to the world of this novel and the way that it is sharply delineated between the two sides, you will see that Ponyboy gives us a clear description of the Socs and Greasers and the characteristics that each group possesses. Note what Ponyboy says:
We're poorer than the Socs and the middle class. I reckon we're wilder, too. Not like the Socs, who jump greasers and wreck houses and throw beer blasts for kicks, and get editorials in the paper for being a public disgrace one day and an asset to society the next. Greasers are almost like hoods; we steal things and drive old souped-up cars and hold up gas stations and have a gang fight once in a while.
So, if we examine this quote, it is clear that the two central differences between the Socs and the Greasers, according to Ponyboy at least, are the way in which the Socs are richer and occupy a higher social class than the Greasers, who are poor and working class, and the exact nature of their delinquency, which, according to Ponyboy, is just trivial on the part of the Socs but slightly more serious when we consider the Greasers.