Buying is easy. When to sell is the hard part. i don't know if I can answer your question. Different trades have different strategies. In the QQQ day trade I would like to see a 20-30 ceny reward potential for putting 10 cents at rsik. If I have a profit and see the program trades seeing follow through buying I may cover early. Selling also depends on how closely i am following the market.
Do I go long? As i do. I will not carry a long position home at this time. Sometimes I do a short. I am short QQQ now, over the weekend. I do have a bearish bias to my trading, but following the tick makes me more comfortable being long.