Should I Treat All Long-Tail Keywords The Same?

Some long tail keywords may have, say 20,000 competitors, while others may have 10,000 (for example).

My question is, do you use all of them the same? Meaning, for example, do you want to dedicate entire blog posts/pages to the long tail keywords that have 20,000 competing webpages or more, while simply sprinkling-in the 10,000 competitor-or-less long tail keywords?

Are there competition or number-of-monthly-searches thresholds where you want to use different long tail keywords differently than others?

Or do you just simply want to use as many of them as much as possible, with no method to the madness?

Some search engine recommends a non-empty meta keywords tag less than 874 characters.

It should be a ratio between competition and number of monthly searches. Look at the ratio for several keywords and take those which are more interesting first, then proceed, but the important thing is to create original content (pages) for each one.