Apart from what @SA has mentioned , I would say learn about
flex box. By the time you would grasp the details of responsive design practices , learn flex box next and it would be supported in all major browsers.
For now here are stats :
Can I use : Flex Box[
^]
It already has 68.36% support and 14.29% partial support for browsers and by including fallback techniques , you can use it in production environments too.And the best part is , once you've mastered it , you'll no longer stressing about widths and heights of your webpages.
Here's a detailed version that would help you :
A-guide-to-flexbox[
^]
Another thing I would like to point out is , WDesigners currently is moving away from fluidic/liquid design and instead adopting the
Show-What's-Necessary approach. For example , fluidic design deals with arranging all elements of a desktop website to a small screen device , but for latter approach , it includes hiding unnecessary elements and showing only those which are necessary. Designers can choose to show specific elements on smaller screen and hide them on bigger ones and vice-versa. At the end , you'll end up with 2-3 breakpoints + fluidic design approach in b/w them + an UX consideration of showing necessary elements.