Please follow below steps to disable cache for block :

–  layout cache disable:-
1) You can use cacheable=”false” attribute in your layout to disable cache for a block but problem is that it will disable whole page cache.

<block class="QaisarSattiHelloWorldBlockHelloWorld" name="helloworld" cacheable="false" />

2) Another option for cache diable

<block class="QaisarSattiHelloWorldBlockHelloWorld" name="helloworld"  ttl="30" />

– programmatically cache disable :
Disable cache for block programmatically:-

<?php
/**
* Simple Hello World Module
*
* @category QaisarSatti
* @package QaisarSatti_HelloWorld
* @author Muhammad Qaisar Satti
* @Email qaisarssatti@gmail.com
*
*/
namespace QaisarSattiHelloWorldBlock;
class HelloWorld extends MagentoFrameworkViewElementTemplate
{
public function getCacheLifetime()
    {
        return null;
    }

}