Make sure you focus on learning the fundamental concepts instead of a particular language or technology stack.

There are many debates online on what you should learn. The truth is that you will be required to learn new technologies for different companies in your career. So, you should focus on transferrable knowledge: fundamental concepts.

Avoid tech debates. Is iPhone better or Android better? I’d say both do the same job pretty well in different ways.

You can choose any modern tech stack and start learning the fundamentals.

Web Development

Web development is about building websites and web applications like Facebook.com and Twitter.com.

There are two parts to web development: front-end and back-end.

Front-end is everything you can see and interact with on a website. You will need to learn HTML, CSS and JavaScript.

Back-end is everything you don’t see on the website: databases, business logic, user management, etc. You will need to learn any one of the following back-end languages and frameworks:

• Ruby on Rails (used by many startups)
• Node.js (JavaScript but for backend; used by many startups)
• Java (used by Google)
• PHP (used by Facebook)
• C# (used by Microsoft)

How should you pick? You can choose any one of them. You just have to make sure you learn the fundamentals. Personally, I think Ruby on Rails and Node.js are more beginner-friendly.

By the way, if you know front-end web development, you can build mobile apps too! Read on.

Data Science

Python and R are the two major languages in data science and analysis.

Many of the common tasks can be achieved in either of them.

Your task is to learn data analysis, so make sure you retain that knowledge. Once you can use Python, you will have little problem picking up R, and vice versa.

In this case, when in doubt, toss a coin.

Mobile Development

This one is easy.

If you want to build iPhone apps, learn Objective-C or Swift are for Apple’s iOS.

If you want to build Android apps, learn Java.

Alternatively, you can use React Native to build both iPhone and Android apps. React Native is a web-based technology using JavaScript, so if you know front-end web development, you can build mobile apps too!

If you are a beginner, it doesn’t really matter as long as the tech stack is widely used in the industry. You have to be able to transfer your fundamental knowledge across different technology stacks.