Why you're not improving 3x3?

Your Cube does not matter
Yes it is fun to binge cube reviews by TheCubicle, but ultimately, the cube you are using is not going to make you faster. Unless you have a Rubik’s Brand, then you should focus on the basics of cubing to get faster.

Look Ahead
When I was averaging around 20 seconds, I remember watching an old youtube video from Chris Olsen AKA Cyotheking that was titled “[Pro Tip] How to Improve Rubik's Cube Look Ahead”. This video helped me improve to around 14 seconds. To summarize the video, Chris talks about how you should do slow solves to improve your look ahead. Slow solves allow you to focus less on the pair you are currently inserting, and more so on the pieces moving around that pair. While doing slow solves, try to not pause or do any unnecessary U turns. You might find out that doing slow solves would get you the same times if we were going full TPS.

Learn the best Algs
The algorithm you are using to solve any case should be the most efficient. Efficient means less rotations, less moves, and incorporates the best finger tricks. For me, I could tell if the algorithm was good by the way it slipped off my fingers. You can go to the top of the website to find the best algorithms to use!

That is it for now, maybe I will add more tips to improve later.