I am not yet a successful trader but I aim to be one. One thing I do so that I can prevent further losses is to have a trading plan always. I cut my loss when  it reach 10%. I don't want to wait for long and I saw some coins dip as much as 90% so to avoid further losses, I would just cut it when it reach that price. I have a risk reward ratio so even if I cut my losses, I would just wait for it to settle in a possible support and go in range and then find a good entry price. I know that others may advise not to sell because it is just unrealized loss but I don't intend to wait that long. I am not just a long term hodler.