1. Download less-1.7.0.min.js from LESS site and add to your scripts folder.
2. Open HTML file and add the line.
<script src="Scripts/less-1.7.0.min.js"></script>
3. Using Visual studio, create .less file and add line to HTML file before js-files.
<link rel="stylesheet/less" type="text/css" href="Content/custom/css/hello1.less">
4. Open web.config file and after(underneath) <system.web> add
<system.webServer>
<staticContent>
<mimeMap fileExtension=".less" mimeType="text/css" />
</staticContent>
</system.webServer>
Now you can play with .less files in .NET environment.