hi please give me an idea to find and fix the best trailing stop value
It depends on particular instrument and its current volatility. The main idea is that you have to stay in position without being stopped out as long, as possible. At the same time, you have to close position in case of reversal.
As usual, trailing stop size could be based on usual stop size meaning that you set appropriate stop and then it turns into trailing stop. You can also find the most suitable value through backtesting different ones using special software like Forex Tester to check it on historical data. Each itsrument has its own volatility, so you can find the balance by checking different values. The general rule is that size of the pullback should not exceed the 1/3 of the whole movement, but in the most of the cases it is better to use shorter stop.
A common guide to trailing a stop is to start trailing it when the unrealised profit reaches the same amount as your initial risk that would have been lost if your stop-loss had been hit. so imagine you have a stop-loss of -£100: as soon as your position reaches +£100, your trail your stop to your entry price, then move it every time price advances so that your stop is always £100 behind the current price.
This is OK, but the TA which decided your initial stop-loss should be X pips behind your entry is now long gone and not relevant. So a trailing stop at a fixed amount like this will always incur the maximum risk which is maybe not necessary. so you could also use new TA features like support or resistance as they appear to set your trailing stop - as long as these are never more than -£100 max.
A trailing stop means you will never lose big but you will almost certainly never win big through running a winner on a long-term trend or pyramiding your winning positions.
The trailing stop loss order can help make the decision to sell easier, more rational and less emotional. It is designed for who wishes to minimize risk, helping him or her minimize losses while maximizing potential gain With the trailing stop loss, it all happens automatically, so you and your trader don’t constantly have to watch the stock price.