If you have a good idea for an app, and the skills to create it, then producing your own premium app can be profitable. However, with so many free apps available, it may be hard to convince people to pay. If you want to go down the premium app route, consider having a basic free version to encourage people to download the app in the first place. You can then provide the option of upgrading to a premium plan once users realize how useful the app is.
Whatever you choose to do with this monetization and marketing technique, take time to plan your strategy. While it is very easy to get started and to add Amazon affiliate links to WordPress, the key to success is in how well you execute those links and promote them to your visitors. Affiliate marketing takes time to excel at, so be patient and don't give up!