Hello there! I've been doing thousands of banner ads over the last 20 years. I've learnt with experience and after trial and error as they said. There are many things you can try, but the basics are very simple, if you like I can share my experience:
- When you work in advertising, in general, people are against you. They're reading their blog, or website and don't want to be bothered by ads. So you would like to keep it simple and not overload the banner with information. Short texts, simple messages, clean images.
- Avoid using flashy things to catch your audience attention, if they are interested and you can explain your reasons, they'll probably click! Play nice
- Always check with the network or publisher the requirements. In my case, 90% banners are GIF format, only repeat 3 times and last less than 10 seconds. A border is required. Acceptable weight is around 100 kb. Banners will stop and be fixed in the last step, so that's where you want the most important information to be.
- Always try to include a button or 'call to action' to encourage people to click and know more.
- Hype is a wonderful tool to build more attractive html5 ads. Other than that you'll have to use Google Web Designer. To be fair that app has improved a lot during the last years but Hype is much more easy and reliable to use. You can develop smooth animations and improve image quality a lot. Also, weight limitations increase for html5. Check with the publishers.
- All other rules you already know about graphic design or advertising apply. Just keep it simple as when you are designing a billboard in a highway and people do not have much time to pay attention to it.
- In general, the elements that I use in any banner will be: a claim and perhaps a subclaim, around 5-10 words each. An offer (discount, or price). Product or brand logo. A CTA (call to action) button. One, two or three background pictures in two or three different frames that will repeat. This may change a lot depending on the industry you are working with, I'm mostly working travel and hospitality stuff. If you work retail you may want to present the products again a clean background, no pictures.