Source: techripon.com

Blogger Method:

• First of all login to your Blogger Dashboard
• Open Your Template’s HTML Editor
• Press Ctrl+F and search for </style>
• Then simply copy the below code and paste just before </style>
• Save the Template

@media only screen and (min-width: 310px) and (max-width:500px) {
#adBottom {
left:0;
position: fixed;
text-align:center;
bottom: 0px;
width:100%;
z-index:999;
}
}

Now Go back to Blogger Layout

• Add new Gadget
• Select HTML/Javascript Gadget
• Now Copy Below Code and Paste it there.

<div id="adBottom">
Your Ads Code Here
</div>

Now go to your AdSense and Create a new Ad unite

• Select fixed size
• and enter the size 340×100
• Now copy the ad code and replace it with “Your Ads Code Here“
• Save the Gadget.

That’s It.

WordPress Plugin

Here is a Great Plugin Called Adace

You can download and use it for free from Here.