Slumps are a natural part of anyone's trading career and should not be feared with trepidation. Even the best traders are prone to getting in slumps, just like the best baseball players are liable to go cold for periods of time. The traders who will have long and successful careers are those who are able to limit the damage during these difficult periods and adjust to get out of the rut.
The first step is recognizing when you are not seeing things clearly or your approach is not working. If you make several bad trades in a row and/or have a few bad days in a row, take a step back. Get up from your desk or take a day or two to simply watch the markets.
Second, cut down your size and reduce loss limits. Some talented traders make money 90% of the year, but lose all that money back during slumps. When you're not trading well, do not let yourself get hurt badly. Huge losses when you are trading poorly not only dig a deep hole, but also damage your psyche and confidence.
Third, only trade your A+ set-ups. You should always be selective, but when you are struggling place an extra emphasis on being patient. If you only focus on the best set-ups, you are more likely to again become positive.
Fourth, set short-term goals. Do not focus on how much you are making, but rather focus on simply getting green again. Even if it is $20 a day, discipline yourself to be positive every day before later attempting to build yourself back up.
Lastly, be realistic and honest with yourself. If you find yourself losing money, have the self-awareness to take it easy. It will take time to get out of a slump, so do not rush things and try to make everything you lost back. The biggest thing is to not fear a slump.
Many people cannot get out of a tough stretch because they become crippled by getting into a hole. Slow yourself down during a slump but have faith in yourself that you will turn it around. If you can limit the bleeding during bad stretches of trading, you will easily be able to make that money back and more when you are on.