There are several ways to determine the appropriate stop loss and take profit levels that will formulate a risk management plan. When you are day trading the goal is to exit your positions before the day ends.
This means you should know how much each security you plan to trade, moves per day.
You can start by determining the daily volatility of the product you plan to trade. This will give you an idea of how much you can make or lose on average during a day. You can calculate this information yourself or look for it online.
If you are trading forex you can look for the amount in pips, or percent. If you are trading stocks the volatility might be in dollars.