You should know what you want to do with it before you enter the trade. You should have an idea of how the trade will play out, and how you will react to how it does actually play out. If the market suggests that it will continue to rise, you hold. If it doesn't, then you sell. You can always re-enter a trade, and you should always be in it for a reason. If that reason disappears, then you should no longer be in the trade. My opinion of course.
I lost some money by assuming that this was the case. A company which I was looking at publicised some good news, I got in, and the SP tanked. From what I understand, this can happen even if the news seems good...but not quite as good as investors expected. I don't bother with news any more, prefer to work off the charts.
disc: I'm a newbie too and have only been trading for about 6 months.