Here are a few points I’ve noted from my experience trading with EAs.
1. An EA is a robot. Robots do what we program them to do. Apart from bugs or malfunctions they do not make psychological mistakes like us.
2. Have a long term financial plan (3-5 yrs) then try to incorporate your EA into that plan. You’ll be amazed how quick those years go.
3. If you are trading an EA that has proven profitable over time don’t be in the habit of looking at your account balance all the time. Find something else to keep you busy.
4. Simple answers to simple questions:
• “Why did the EA exit here instead of here?” Because it did.
• “Why did it not enter here?” Because it didn’t.
*Refer to
point 
No.1
5. All good trading systems
will have losses. Its the monthly statement that counts. Anything claiming no losses is not worth your money. The same goes with EAs.
6. Do not decompile EAs if you cannot afford them. Sooner or later you will lose money. Without updates and support, that EA will bulk on you. Besides only the proprietor knows what the EA truly does.
7. Do NOT change your settings when you get a loss. If those are the recommended settings and you’ve been getting profits with them, stick to the plan.
8. Please do not increase your
leverage 
to regain losses.
9. Join forums with traders using the same EA, ask questions and give comments. You will learn a lot.
10. Last but not least. EAs are not get rich quick schemes. We all need money, but it doesn’t grow on trees; it grows like trees. Anything that can make you retire overnight can also make you a pauper just as fast, so be careful.