I would go further than that - define your entire trading plan. Your goal, your strategy, your risk, you account, your stop loss, you trading hours, etc. Define them before you invest.
It is very important to set goals in trading. Success is never achieved without a goal set. Because if you don't know how far you want to go by trading, then how do you meet that goal. Proper money management and risk rewards must be followed to move towards the target.
I find it hard to set goals because of my inconsistency on a day by day basis. It no good for me to say I am going to earn 2% today as one day I am up and the next I am down. I think goals need to be set for longer-term like monthly or quarterly..