@Alexaxel98 as @PortableStick mentioned, FCC is not focused on design, it’s more about coding. However, you may find a lot of awesome design tips asking for review on gitter or in other FCC related places.
I always start thinking mobile first.
Why? The main reason is that if you have your sketch, prototype, wireframe, etc fitting mobile, you should start with the most important stuff. On larger screens you can simply add more, reorganize stuff, or simply make stuff appropriately bigger and with more free space around.
When somebody starts desktop first, it seems harder to reduce the number of items. This approach is also great to train UX and product management skills. Design a product (whether it’s an app or a simple website) from the smallest display possible. It puts a lot of constraints, which is sometimes harder than simply code desktop first.
Designing mobile first, keep in mind horizontal and vertical display differences. Sometimes what makes sense vertically gets cut horizontally and a small change in design may make it work better.
What’s more, it’s not just mobile. It’s mobile first, touch first, and user first. Not only mobile devices have touch sensors.
Despite all above, sometimes the projects are to be redesigned. Don’t treat projects as finished stuff, iteration is the king and good product is never done. Be open and give a chance yourself to get constructive feedback from others. It makes us grow. If I don’t have time to introduce changes today, I will keep it on my to do list for the future and come back later. Loving own designs and code too much may be an obstacle to code and design better.