Don’t twist the light too tight, makes it extremely hard to untwist. Especially when it’s a smoothish light. What I found works is to take some painters tape or some kind of similar tape, duct tape might work, it’s pretty grippy. Well you wrap the light in tape then twist apart.
Don't shake a non-working high powered light, while looking at the led. It will turn on just about every time.
Don't short the positive and negative leads of a NiMH battery pack together, even by accident, because you left the bared wires uncovered and they touched (and immediatley welded together, while the batteries got so hot the wrapping started to melt, while you tried to find the dykes to cut the wires apart).
Don't strip wires with an exacto knife... towards you.
Remember... Anything not lying on the floor, will end up on the floor, before you can reach it as it falls. (Especially if it can break when it hits the floor).
Don't try to grab the hot end of your soldering iron, when it starts to fall on the floor. Just let it fall!
Don't use the same color wire for Positive and Negative, from the driver, to the led, as you have a 50/50 chance that you will wire them wrong at the led side.
If you have a reversible drill, make sure you know which way forward is... It's probably not a dull drill bit.
I'm just sayin...
Don't try to bore a light by hand or with a drill and sand paper ..it's about the dumbest thing you'll ever try ..
Don’t wipe your bum with broken glass.
Don’t eat yellow snow.
Don’t ask a question, then find a solution elsewhere and just terminate the thread with “never mind”.
If a square peg won’t fit in a round hole, your hammers not big enough.
Also never assume the soldering iron has cooled down enough to rest it on your leg...
Buy a DMM (digital multi-meter) and test your batteries.
measure twice cut once.
use thread lube on your lights...keeps 'em from feeling el' cheapo (ref)
on your dive lights use silicon grease regularly to keep 'em waterproof & preserve the o-rings.
in general smaller lights get more use
If your P60 drop-in normally runs on one 18650 make sure it can accept 2 x CR123A cells (6 volts) before attempting
Cheap chargers may continue to charge after indicator light is turned off, thus overcharging battery.
Don't believe the lumen/lux numbers unless you see something like ANSI
realize that you're in one of these stages of flashaholism. you may want to just jump to the end stage and call it good...
Progression:
Newbie: I’d like to get a brighter AA flashlight
Intrigue: I can use another light
More Intrigue: and another
Power hungry: Hummm these Li-ions give me power… want more… more POWER!
delusion: I have the ultimate in PoWer… nothing can beat this light!
Tint snob: I notice these lights have a shade of purple or green tint
Elitism: These lights disappoint me. CRI. What is CRI? (inspired by CPF post)
Ok scaru (post below) I added some more 
I don't think it's a good idea to cut a battery, no matter the voltage. 
When buying cheap lights from dx:
spot a new one you really like, don't wait for others to review or comment, ignore a lot of the claims but do have a very good look at the pictures to asses the quality, and buy it. 1) it is fun to be the first to have a look , 2) (so I have understood in this forum) the first run of a new light is sometimes of better quality than later runs of popular lights.
For a noob like me, these are wise words indeed. They seem to be born from experience! :bigsmile:
Your fences need to be horse-high, pig-tight and bull-strong.
Keep skunks and bankers at a distance.
Life is simpler when you plow around the stump.
A bumble bee is considerably faster than a John Deere tractor.
Words that soak into your ears are whispered...not yelled.
Meanness don't jes' happen overnight.
Forgive your enemies; it messes up their heads.
Do not corner something that you know is meaner than you.
It don't take a very big person to carry a grudge.
You cannot unsay a cruel word.
Every path has a few puddles.
When you wallow with pigs, expect to get dirty.
The best sermons are lived, not preached.
Most of the stuff people worry about ain't never gonna happen anyway.
Don't judge folks by their relatives.
Remember that silence is sometimes the best answer.
Live a good, honorable life.. Then when you get older and think back, you'll enjoy it a second time.
Don't interfere with somethin' that ain't bothering you none.
Timing has a lot to do with the outcome of a Rain dance.
If you find yourself in a hole, the first thing to do is stop diggin'.
Sometimes you get, and sometimes you get got.
The biggest troublemaker you'll probably ever have to deal with, watches you from the mirror every mornin'.
Always drink upstream from the herd.
Good judgment comes from experience, and a lotta that comes from bad judgment.
Lettin' the cat outta the bag is a whole lot easier than puttin' it back in.
If you get to thinkin' you're a person of some influence, try orderin' somebody else's dog around..
Live simply. Love generously. Care deeply. Speak kindly.
Long hair don't hide a red neck.
Don't pick a fight with an old man. If he is too old to fight, he'll just kill you.
Amen, guyz :bigsmile: Great tips 
Don't ask questions you already know the answer to.
Don't ask questions you don't want to know the answer to.
Don't look down on other people unless you're helping them get up.
It's better to fail miserably at something than not to try at all.
Nah, Old-Lumens is too smart to have actually done any of that. 8)
Oh yeah: never pass your hand under a soldering iron that has a big glob of solder on the tip….
Make sure you don’t use your DMM that you have set up for Amperage reading to check a batteries voltage, those tips get hot real fast and they do burn your hands, don’t ask me how I know 
Don’t use your finger as a heatsink when testing XM-L’s… :~
Always assume the soldering iron is hot!
Oh, I’ve done them and many others as well. It’s called “experience”. When someone tells you “I know from experience”, it means they learned it the hard way and you will to… It’s human nature
I knew this was going to be a good thread. Thanks for sharing!
I'm assuming/hoping you found a better way. Care to share?
When you have a 3P pack of batteries don't just chop through the wire, that will short it out...