How do you practice without a coach or by yourself?

Your technique has to very good to practise technique whitout a coach. If your technique is good how would you improve without a coach. You Will properly train your bad technique

I train during the matches. If I play with someone of above level, I just try to make as few unprovoked mistakes as possible. If I play with someone of below level, I try to win points or test shots whenever possible. Always try to catch any point possible by proper positioning

Wall practice is your friend. Find a wall and work on volleys, drives, and positioning. Also try recording yourself playing matches to spot patterns in your mistakes. I built PadelTracker to help analyze match stats, but for technique the wall is honestly the best free practice tool.

Shadow padel: you imagine yourself in a match situation and drill a certain shot with a racket and without a ball. You repeat it 50 times per shot so that your muscle memory internalizes it. Of course there's the risk that you repeat the wrong thing and your body learns it without a coach's feedback. So you can have a coach show you the proper technique first and then go home and imitate this movement without a ball.

Wall practice is definitely the way to go, especially for volleys and drives. Focus on consistent contact point and follow through. Portugal has some great club walls that work well for this. For positioning, try playing against stronger opponents when possible - you'll learn defensive positioning faster than any solo drill can teach.

Ball machine?

Get some coaching, focus on translating that to your normal play... same as golf.