After 4 years of experience in which I endured much loss and still enduring loss now I can say that mamy traders forget to use the stop loss or use it in a incorrect way.
The finest way I know is that how much profit you are taking on that trade and how much loss can you accept.
If you want to imcrease your profit you would also need to increase your stop loss in a way which is acceptable to you because while trading we forget that it is a business like any other business you would need to take precautions.
One way of using a sl (stop loss) is that if you want 10% you would need to have sl at 5% but if 5% is more you should reduce it but you will need to reduce the profit to increase accuracy and another way is to risk min and earn max through trailing sl or high risk reward trade in which you would profit 10% but will risk 2%. It will effect your accuracy but you will succeed in both strategies in the long term as you will trade high probability set ups or you will trade less probable setups in the first option but will earn good.
in next few posts everything would be posted about how to use the sl in right way as this post is to give you min knowledge about stop loss