For those who have experience flying the phantom long distances, what are the essential tips and tricks to keeping it safe and reliable?

I am by no means an expert in long distance flying but from my experience it is always important to keep a clear and unobstructed line between you and the drone. One thing I'm noted when flying in populated areas is the Wi-Fi and cellular towers can cause you're drone to experience interference at close distances  end it may not be related to how far out you are.  Also if it is possible I like to fly upwind if I am flying far away that way if I'm running low on battery the wind will help me on the return flight.  But it is important to note that according to the FAA laws you should always maintain visual contact of the drone...

Of course because I have bionic eyes!

Factor the wind in to your flight planning and if the wind is moderate or higher, never fly away downwind because it's going to be a headwind coming home.
Always use caution and factor in a safety margin.  Aim to be back on the ground around 30% battery.