You’re right about not using batteries with any noticeable physical damage or torn wraps. About the .08 limit...that depends on what batteries you use, type of coil, vaping style, and personal preference. (Ex: Sony VTC5a’s are work horses and I’ve built down to .04 with them, certain coil builds take longer to heat up than others...if you use a very fast ramp up time type of coil, you’ll practically be pulsing rather than holding the fire button down..with pulsing you can get away with a lower Ohm build, and then if you prefer a cooler vape you can build higher or use coils with a larger mass that take longer to ramp up).
Cleaning is important, too, on the exterior, not so much (in fact some mods look better with some patina going on), but your button assembly, threads, and all contact points should be taken care of to keep any grime or gunk building up and causing more voltage drop which will cause a drop in performance. Also make sure any vent holes are unobstructed and clear. Make sure the tube itself on the inside is taken care of and there is nothing protruding or sticking out that can tear your battery wrap. Make sure any atomizers you use have a good protruding 510 pin, especially if using it with a hybrid connection device. By wary about carrying any device that doesn’t have a lock mechanism in your pocket and when setting it down to avoid auto-firing. If there is an adjustable pin for battery rattle, make sure it’s used correctly so that your battery isn’t banging around in the tube, but not so tight that it causes the mod to easily auto fire. Until you are used to building coils and knowing what they Ohm out to, don’t build on the mod...an Ohm tester should be used for building and checking your ohms out before trying it on your mod.
Keep an eye on your batteries for any black dots/marks that indicate any arcing going on.
Try to avoid draining a battery down too low...once you have a noticeable drop in performance swap out for a fresh battery. Be careful with overdripping too much as the liquid can sometimes get in the tube and all over the batteries. I’m sure I’m missing some stuff and a lot of that stuff is pretty common knowledge for anyone, but better to be safe than sorry...we have to make sure not to give the media anymore reasons to vilify the vaping community because someone builds, essentially a pipe bomb and takes off their face and hand!
You're not drinking water are you?! You realize that stuff is found in antifreeze!?!