Reversal in forex is the point at which the market turns against the prevailing trend whether in a positive or negative direction. Reversal can be noticesdepending on the type that wants to occur. It can be through 

DOJI, ENGULFING PATTERN, PIERCING LINE,or 3 LINE STRIKE

DOJI represent indiscision and its denoted with + sign. If the market is going bullish and you are following the trend and at a point you see a doji+ sign, be a alerted because it might apperar that a reversal is going to happen and the bears might take the market.

ENGULFING PATTERN can also be used to notice reversal sharply. If candles opens and engulfs the previous candle. i.e  larger than the previous candle in width,reversal is eminent. The type of candle that opens will determine the trend .

PIERCING LINEis a good indicator that reversal is eminent but it is good to wait for another reversal before jumping into conclusion.when you have a partial candle eg 5-6 bearish candle on a spot and a bullish candle comes up at least 50% of the previous candle,piercing line is confirmed and its a sign that reversal might occur.

3 LINE STRIKE involves 3-5 candles and they are not often seen in the market but once its spotted,trend should be followed because its a guaranteed reversal. when 3 to 5 candles opens and they follow the same trend and one last candle opens against them engulfing them all,reversal has occured and the trend must be followed to be better pips up.

The things to consider to follow the right trend is analysing the trends on the basis of its frequency to see the consistency of the movement.you can go on a 3 to 4 hours time frame to check how the market has move in the last few days in the case of secondary trend.

If its a primary trend,.its better to look at a monthly chat to know the upward and downward  movement and the longer support and resistance level.

For immediate trend,analyse the market on weekly  and 4 hours trend and use a 15 minutes or 1 hour time frame as the entry point.