When you’re coding @media queries, you choose breakpoints. Many of you take the easy way out and write just one @media query. If you do that, and your max-width is small (600px), people with tablets and even small laptops might see a very bad-looking version of your page.
This article recommends using these numbers for @media queries: 600px, 900px, 1200px — “and 1800px if you plan on giving the giant-monitor people something special” (which you don’t have to do).
I often code only one @media query (usually max-width: 800px) because I tend to be lazy, and I’m only making examples for you guys. But if I had a paying client, I would write two @media queries for any app — one for phones (max-width: 600px) and one for tablets (max-width: 900px). Lots of people do use tablets much of the time, so don’t forget about them.
I would also make sure my page layout does not get wider than 1200px (that way it doesn’t look stupid on a 27-inch iMac screen) — and I would do that with a container DIV, not a @media query.