The method for sub fractionation depends upon what kind of compounds you are interested in.If you are interested in polar compounds ,you can fractionate the extract with polar solvents like 1.Alcohol 2.Alcohol and water in different proportions,3 Methanol,4.Ethyl acetate and so on with decreasing polarity.If you are interested in non polar compounds Yo can fractionate with non polar solvents like Petroleum ether,or n-hexane,dichloromethane,chloroform,butanone,and so on in increasing polarity.
It depends on what way you wana proceed. Which is the target constituent for your study? Broadly if you want to fractionate, just follow the polarity of solvents. For example, start with pet ether / hexane, followed by ethanol/ methanol and then water. Later you can do sub fractioning of the alcoholic extracts to get more fractions.