What should viewport be set

In most cases, the viewport should be set as:

<meta name=viewport content="width=device-width, initial-scale=1">

Never use minimum-scale, maximum-scale and user-scalable, unless you really need them. By using them the users may not able to zoom the page in the way they want

And never set initial-scale to other values than 1, unless you really know what are you doing here. Below are the screenshots captured from a mobile phone, which will explain why you should use 1 in most cases

initial-scale=1

initial-scale=0.2