Learning from Profits and Losses

On one level profits vindicate analysis and losses are to be expected.  Nevertheless learning from both to improve future stock selections makes obvious sense.  Are there any common characteristics about winning trades?  Of the losing trades was there anything that could have been avoided...for example a few of my recent losses were buying above my buy range - basic mistake. Once a buy decision has been made I must stick to it.  Though also I need to improve buy levels - so that they generate the most profit - the lower they are the better the profits...but equally if set too low could end up below the low of the next trading day if overnight upward pressure.