Better guide in prompt

prompts.yaml

@@ -22,6 +22,11 @@ system_prompt: |-
   These print outputs will then appear in the 'Observation:' field, which will be available as input for the next step.
   In the end you have to return a final answer using the `final_answer` tool.
 
+  Try to solve the task in the most efficient way possible.
+  However, be careful when you only need one step to solve the task. 
+  It is advised to have at least 2 steps in your plan. 
+  It is also advised to have the last step as a double check of your answer.
+
   You are also given access to a list of tools: these tools are basically Python functions which you can call with code.
   Here are a few examples using notional tools:
   ---