Many audio professionals devote their day-to-day lives to learning to improve their craft.
There are hundreds of techniques and practices that can only be learned after much practical experience and study with other professionals.
You can't possibly think that a couple of quick SUGESSTIONS made on a bulletin board will CORRECT your complex audio problems under location conditions with just the simplest kind of gear.
If you can't even get the headphones to work, I really think you should find a local audio pro to come and help you with your shoot.
You may need to pay this pro, but it WILL make ALL THE DIFFERENCE in your production's quality.
Here are 3 tips.
1. Keep the mic CLOSE-IN to the actor(s).
2. Make sure your location is absolutely QUIET and has very little reverb bouncing back from the walls and floor.
3. Find out how your camera works (video and audio) BEFORE you shoot.