Originally Posted by gav
There is no best online marketing technique. There are different platforms on which you can do online marketing like Google Ads, Facebook Ads, Bing Ads and other social media platforms where you can show up your paid apps in the best way you want. Also you need to be active on various social media platforms and share the news of your products and services through them. Also you need to think on which platforms your targeted customers can be best found.
I think you are just talking about Online Advertising, not online marketing as a whole.
for me, I think SEO is a necessary practice to do when it involve online marketing. Optimize user's experience on your site is also important (Google analytics could help you with this)