It's been a big news week – and a long one for ill-served viewers. Here's a survival guide from one weathered veteran

The marathon coverage of the Boston Marathon bombing has set into motion the all-too-familiar. When something awful happens, the human impulse is get informed instantly. That often means rushing to a TV and gaping at the unfolding drama. It's an understandable reflex, but usually, a self-defeating one, like scratching a sore or drinking sea water.

It may satisfy the immediate urge, but beware the consequences. CNN's false report about arrests was as predictable as it was irresponsible; live TV coverage is a world of blunder. So, if you must tune into 24-hour cable news for the latest, there a few things always to bear in mind:

A watched pot never boils. Following violent crimes and disasters, the intensity of the coverage is inversely correlated with the prospects for advancing the story. Incidents last as long as they last – usually, seconds – then they are over. The "when" and "where" and some of the "who" (victims) are immediately obvious. The rest of the "who" (the culprits, the missing), plus the "why" and the "how", can take days or weeks or months to unravel.

The latest developments usually aren't. Desperate to add to the endlessly repeated basic facts, reporters will breathlessly pass along tiny bits of detail gleaned from authorities speaking unofficially, possible witnesses and cousins of possible witnesses. Do not be fooled by the urgency in the journalists' voices. The details are second or third hand and usually wrong. "Unconfirmed report" means "not true". "Confirmed report" means "probably not true".

Get your brain a screen saver. That's what computers use to keep a single image from being etched into the screen. If a tragic news event is caught on video, TV will show you again and again what happened until it is forever burned into your consciousness. Eventually, this denudes even the most shocking footage of any informational or emotional clout – not to mention, meaning – and turns it into little more than a GIF. If you absolutely must hang on to every word, consider switching to the radio.

If you knew what went on in the kitchen, you might not eat at the restaurant. The cable channels have a handful of anchors and a handful of reporters. They may look authoritative, but they don't constitute anything remotely like a robust news-gathering machine. The channels do employ a whole mess of producers, but their principal job is to book experts and pundits, who may have credentials and make-up, but are basically just guessing.

Bad news does not necessarily have larger significance. When calamity erupts, your favorite network will be live on the scene for hours or days. Logos will be designed. Concern will be etched on the anchors' faces. Thoughts and prayers will be expressed for victims and their kin. But neither the amount of airtime nor even the body count are reliable measures of intrinsic importance. A fatal spasm of violence (in the west only), or a mass shooting, or even a missing blond person (if cute), will always trump, for instance, a budget vote or telecom lobbying or other events lacking yellow police tape that affect a large percentage of the population every day. As the saying goes: if it bleeds it leads. The corollary is: Citizens United – the supreme court ruling that fundamentally altered the scale and transparency of US political campaign funding – didn't get a logo.

They shoot horses, don't they? You've seen film of the dance marathons from the 1930s – those desperate people circling the floor for hour on end, day and night, in the hopes of winning some pitiful prize. When you tune into 24-hour cable after a tragedy, ask yourself the question: "There is nothing being accomplished through this awful spectacle, so why am I watching?"

© Guardian News and Media 2013