Use a device that reads ohms to check for shorts/low ohms, THIS IS A MUST.
Shorting a mech is bad bad bad and too low ohms can be just as bad. Find out the "C" rating of your batteries (unless someone can chime in with the Efests, I'm not familiar with them) and find out how low you can build a coil.
Don't over discharge your battery past ~3.5v, mechs will vape until you kill the batts. Its fairly easy to tell as vape quality decreases as the battery gets lower and lower, but you'll have to get a feel for it.
Besides the safety aspect of it, the rest comes down to preference. YouTube and ECF are your friend, helped me through having a great experience when I first using mechs. They are quite a bit different than regulated mods, but are easy to get the hang of.
Please someone else come through if I missed anything.