Google AdMob allows you to setup your own Campaigns so you can control what banners appear in your app. This is very useful if you want to sell the banner space to someone or advertise your own product/services.
To setup your own banners
1. Login to your AdMob account: https://apps.admob.com
2. Click Campaigns (left-side)
3. Click Create Campaign
4. Select “Direct Sold” as the Campaign Type
5. Select the Goal that you want for that banner ad. The Goal depends on how often you want their banner to appear. If you want their ad to appear all the time, select "Percentage of Impressions." You can also select "Percentage of Impressions" if you only want it to appear 50% of the time. If you only want to give that banner ad a certain number of impressions or clicks, you can select those Goal types too.
6. Select Ad Units (check the boxes next to each app listed and click Confirm)
7. Click Continue
8. Enter a name for the Ad Campaign
9. Enter a % of total impressions that you want to give that add (i.e. 100%, 50%)
10. Select a Goal Schedule. This is how long you want the ad to run
11. Click Save & Continue
12. Click the Create New Ad and select what you’ll be advertising
13. Enter the information for a Text Ad or Upload your own banner. The dimensions are 300 x 50.
14. Click Create Ad