1. Create a favicon, from a image/logo that you like then with Favicon from Pics convert it in .ico or gif file.
2. Upload it in your host root, if you don't have a host, I recommend you to use imageboo to host your favicon.
3. Now that you have your URL/link of Your Favicon, you need to add it in your template. For this login to your blogger account, then click on Dashboard >> layout >> HTML.
4. Press CTRL+F and make a click inside of template HTML code and search for this tag </head> and just above it paste this code
<link href='http://your.link.com/yourfav.ico' rel='icon' type='image/x-icon'/>
<link href='http://your.link.com/yourfav.ico' rel='shortcut icon'/>
<link href='http://your.link.com/yourfav.ico' rel='shortcut icon'/>
You will see something like this
]]></b:skin>
<link href='http://your.link.com/yourfav.ico' rel='icon' type='image/x-icon'/>
<link href='http://your.link.com/yourfav.ico' rel='shortcut icon'/>
</head>
<link href='http://your.link.com/yourfav.ico' rel='icon' type='image/x-icon'/>
<link href='http://your.link.com/yourfav.ico' rel='shortcut icon'/>
</head>
Note: if the icon is in .gif format, change type='image/x-icon'/> to type='image/gif'/>
5. Save your template.
If you need more help, don't be shy about leaving a comment below. (: