Relative Strength Index is a non trending indicator. In this chart (Refer the chart)
RSI>70 Indicates lot of people are buying the stock and it indicates lot of Strength should go for long.
RSI<70 indicates the characteristics of over bought Temporary weakness need to sell (Short).
RSI<30 indicates lot of weakness/Selling happening need to go Short because lot of selling happening.
RSI>30 indicates already it is oversold and temporary movement on upside is expected so need to buy the stock.