Next.js has changed the way I make web apps. This is what I wish I had known before I started

I remember when I first switched from plain React to Next.js. I thought it was just React with a built in router. A small update. A layer of convenience on top of something I already knew. I was wrong. Next.js is more than just a framework, it’s a whole new way to think about how web apps are built, displayed, and sent. And it took me longer than I would like to admit to really understand what I had.
If you’re new to Next.js or thinking about it, here’s everything I wish someone had told me on the first day.

It’s not just React with routing.
This was my first mistake, and it cost me weeks of confusion.
Yes, Next.js lets you route files. But more importantly, it lets you decide when and where your code runs. Some code works on the server. Some runs on the client. Some runs while building. Some run every time you ask for them. Before you write any Next.js code, the most important thing you need to know is the difference between these two things.
With plain React, everything happens in the browser. The user downloads your JavaScript, the browser runs it, and the page shows up. Easy to understand, but not very useful.
Next.js completely goes against that idea. And once you know why, you can’t go back.

Server Side Rendering, Static Generation, and Client Side are the three main types of rendering that Next.js offers. The most common mistake I see developers make is picking the wrong one for the wrong page.
During the build process, Static Site Generation  creates your page. The HTML is already built and sent right away from a CDN. For content that doesn’t change often, like marketing pages, blog posts, and documentation, this is the fastest way to get it to you. SSG is almost always the right choice if your data doesn’t change based on the user or the request.

Every time you make a request, Server Side Rendering renders your page on the server. The user gets fully rendered HTML, which is great for SEO and for pages that need new, personalized data. But every request goes to your server, which makes latency and costs go up. Use SSR when the data needs to be current and is unique to the user or request.

The browser does all the work when you use Client Side Rendering . Still useful for dashboards, admin panels, or anything else that needs to be logged in to see where SEO isn’t important and interactivity is the main goal.
Next.js really shines when it comes to Incremental Static Regeneration . It lets you create pages statically, but it checks to see if they are still valid in the background at a set time. You get the speed of static and the newness of server rendering. This one thing changed how I design applications that use a lot of data. Choosing the right rendering strategy per page not per application is the mindset shift Next.js demands.

Again, the App Router changed everything.
As soon as developers got used to the Pages Router, Next.js 13 came out with the App Router. It wasn’t just a new folder structure; it was a whole new way of thinking based on React Server Components.
By default, the App Router renders components on the server. The “use client” directive makes it clear that you want client-side behavior. This means that less JavaScript is sent to the browser, pages load faster, and components can get data directly without using use Effect or external state management.
If you’re starting a new Next.js project today, start with the App Router. Don’t let the learning curve push you toward the Pages Router for comfort.

Data retrieval is not like you know it was.
React Data Fetching React Data Fetching is implemented in use Effect or custom hooks or a library such as React Query. Next.js App Router uses plain async/await to fetch data in server components and simply works.
No use Effect. None of the loading state boilerplate. No client-side waterfall. The component retrieves its data on the server itself and it never makes it to the browser.
This sounds small. It isn’t. It alters your structure of components, your way of thinking about loading states and your caching. Next.js includes an inbuilt fetch cache, which automatically deduplicates requests, can revalidate requests, and works with ISR. The operation of this cache, and the control of it is not incidental. It makes the difference between the quick application and the disorganized one.

The bottom line
Next.js did not simply alter my tooling. It transformed my perception of the server and client dichotomy, the way I think of performance on the first day, and the way I design applications that require scaling.
It has a real learning curve. The ideas build upon each other and the documentation, though excellent in its own right, makes the assumption that you will work out the gaps yourself. But when it clicks and it will click you will know how you could have ever developed production web applications without i.