You can put admob on your android app successfully by following the steps

step1: Register your app in admob and get the publisher id.
step2: Change the AndroidManifest.xml by adding the following lines of code after closing activity

step3: Change the publisher id with yours
step4: Add the following lines of code in main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res/com.test"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/layout"
    >
  <com.admob.android.ads.AdView
       android:id="@+id/ad"
       android:layout_width="fill_parent"
       android:layout_height="wrap_content"     
       app:backgroundColor="#000000"
       app:primaryTextColor="#FFFFFF"
       app:secondaryTextColor="#CCCCCC"
       app:keywords="Android Game"
    />
</LinearLayout>
step5: create a new xml file and named as attr.xml and place in values folder and change it to
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="com.admob.android.ads.AdView">
        <attr name="backgroundColor" format="color" />
        <attr name="primaryTextColor" format="color" />
        <attr name="secondaryTextColor" format="color" />
        <attr name="keywords" format="string" />
        <attr name="refreshInterval" format="integer" />
    </declare-styleable>
</resources>

step6: Download admob-sdk-android.jar and pasted in libs folder and add to build path
step7: Done!!!
step8: For testing add the following lines code into your java file and run...