You can always optimize an expert advisor on a specific chart for a particular time period to find out which input values shaped the highest returns and least possible drawdown. Metatrader?s Strategy Tester lets you you to optimize your expert advisor to get the most lucrative settings for a large number of possible input variable combinations. Though, it is significant to keep in mind that you should not over-optimize. You may get astounding results with a specific input combination, but because the values are so constrained, you probably would not see results like that in future. While optimizing an expert advisor, remember to use your mind and think about the reasons for the results you are getting. Is it from one huge win that you are not likely to see in the future? Or is it wining repeatedly, making it a reasonable trade setup for the future.