Safer Smoking
If you're going to smoke, a few habits make a real difference to what it costs your lungs.
Smoking is the harshest way to take cannabis. You're inhaling the products of combustion, and burning plant matter makes tar and irritants whatever's in it. You can't make that risk-free, but the gap between careless and careful smoking is bigger than most people think, and it's all in your control.
Drop the tobacco
This is the biggest one, and it's specific to how cannabis is smoked in the UK, where most people mix it with tobacco in a spliff. That bolts a second, more addictive drug onto the cannabis: nicotine dependence, plus tobacco's own well-established harms. A lot of what people take for a "cannabis habit" is partly the nicotine talking: the constant reaching for it, the physical craving. Rolling pure, or switching to a pipe, bong or vaporiser, cuts tobacco out entirely. If you find you genuinely can't enjoy it without the tobacco, that's worth noticing in itself. It's covered in Mixing.
Don't hold it in
The belief that holding smoke deep in your lungs gets you higher is a myth. The cannabinoids are absorbed within the first couple of seconds. What the extra holding does do is deposit more tar and expose your lungs to more irritants for longer. Breathe normally. You lose nothing but the harm.
Technique and kit
A few smaller levers add up. Bongs feel smoother because the water cools the smoke, but don't mistake smooth for safe. You're still inhaling combustion products, often in bigger hits, so cooler isn't cleaner. Keep pipes and bongs clean, because stale resin is harsher and dirtier to inhale. Use an unbleached filter or crutch in a joint to keep bits of plant and hot ash out of your mouth and lungs (a rolled card tip does more than the loosely-packed "roach" most people use). And avoid smoking the very end of anything, since the last stretch concentrates the tar.
Where this stops helping
All of this reduces harm. None of it removes it, and it does nothing about the effects of the THC itself. If lung health is a real concern, the bigger move is changing route entirely. A dry-herb vaporiser avoids combustion altogether, and that's the subject of Safer Routes.