It's actually quite simple. Are you satisfied with your profits, or are you still not benefiting from the bitcoins you have.
Don't trust other people when that person suggests selling your bitcoins for a small loss, that's really stupid advice.
You can sell it when you get a profit.
Whatever it is you have to make a target, if it still hasn't reached the target you have to hold it, but when you feel it is enough to sell it.
Don't sell at a loss.