It depends on your goals. My first tip for success would be to understand the various APIs that are available, their capabilities and use cases. It can be a confusing subject.
The Integration APIs are used to embed existing Qlik Apps, Sheets or individual visualizations into a web page. This is done using a URL in an iframe and is a relatively simple and rewarding starting point. This is useful for combining Qlik visuals with an existing page like a company intranet.
The Extension API is used to create new custom visualizations. This is useful for creating a new visualization type that is not available in the Qlik Client. This requires coding skills in javascript and can take a while to get up to speed.
-Rob
