Re: how to write effective display ads ?
I am not sure if you are asking about text ads here or you are looking for the image or display ads.
No matter what the format of the ad is, prime objective of your ad should be to attract the relevant audiences for your business or product which you are advertising online.
Compelling ad with strong call to action which encourages the user to click on it and visit your site's landing page.
Another important aspect of the content of your ad is that you should only speak what you are giving. No wrong expectations, otherwise the user will end up leaving your website without any effective ROI for you.
I wrote one article in the Community last year on ad text tips. You might consider reading it once: https://www.en.adwords-community.com/t5/User-Articles/Ad-Text-Tips/ba-p/50624
Re: how to write effective display ads ?[ Edited ]
November 2013 - last edited November 2013
I try to make ads by answering these 3 questions,
1. What do sell?
2. Why should they buy from you?
3. Call to Action?
That is the text you need to have on the ad. Then you need to have a picture of the product that preferable is eye catching.
This is a pretty simple way to make an display ad.