I often use the RSI Oscillator on my charts to help me predict short-term reversals in price trends. It’s not perfect, but I do think that it at least tells you when a reversal is more likely. If it were perfect or near perfect, then I would be a billionaire and I am not. 
The idea is that the oscillator tells you when prices begin to appear overbought or oversold. But you cannot just go by that. What you really want to see is a divergence where the RSI peaks and valleys are going in the opposite direction from the prices. If the prices are going up, but the RSI peaks are going down then this is a divergence that tells you that the rally is losing steam. Likewise, if the prices are going down, but the RSI valleys are going up, then this suggests that the selloff is losing steam.
Now, recently I noticed another oscillator called the Chande Momentum Oscillator that operates much like RSI, but appears to me to be a lot more clear and seems to show possible reversals more clearly than RSI in several cases. The following chart is a recent 5-min on SPY showing both oscillators.
I have marked the divergences that I saw on the Chande and RSI indicators. It is showing that the next move is going to be down and we are going down slightly but it remains to be seen how accurate the call will be. Now the other thing to realize is that any change that occurs is short-term. On a 5-minute chart, any divergence can only be expected to last an hour or two. It might last a lot longer, but you cannot count on any length. Generally speaking the longer the time interval, the longer the results. So if you are using 15 minute charts, then the result may be 3 times longer than 5-min charts. If you are using a daily chart, then the results would be measured in days. For day-trading purposes I typically use 5-min charts. And even if I’m trading on a daily chart for a longer move, I’ll still use 5-min charts to plan my exact entry.
And as I said in the beginning, looking at the chart I just posted it sure appears like this indicator has amazing accuracy and success, but you need to recognize that it only gives you an indication of what may be likely. There is no such thing as a perfect indicator. If I actually found one of those, then I would keep it a secret and retire a billionaire.