I have read that over 70% of reported night time dreams are of the nightmare sort. That is, they are frightening, scary, or dark in nature. That is a lot of negative angst that must disturb people and cut into the quality of their lives. The following is what has helped me with creating better dreams.
Movies - I do not like terror movies. Watching them has never made a positive difference in my life. I can remember movies quite well and if I watch a violent film, it will stick with me as I go to bed. Instead, I carefully screen what I allow to go into my eyeballs. I try to watch movies and shows with a redemptive quality to them. Or I just turn the television off and find something better to do.
Books - The books I read are usually of the non-fiction variety. I try to stay away from fiction because of the language, ridiculous story lines, and violence. Find a good self-help or biography to read before going to bed. Fill your mind with hope and stories of people who have made it.
Pray - I saw a prayer before going to sleep at night. Prayer is just talking to God. It is how we know we have a relationship with Him. He wants the best for us and so I share my heart with Him.
Scripture - I like to read the truth. I find soul feeding truth in the Bible. After reading it, I try to repeat meaningful portions to myself that will help me keep the right frame of mind.
Relax - It is important to exercise, breath, and relax. Trust that God will work it out. All you can affect is today.
I think it is possible to lessen the amount of frightening dreams at night. Follow the above ideas and see what happens.