To become a good singer without classes, try to record yourself singing, then listen to the recording to see where you need to improve. Then practice every day, singing in short sessions of 10 minutes with pauses between them so as not to abuse your voice. As with any skill, the more you practice, the more competent you become. Athletes, painters and carpenters practice their chosen craft to become as skilled as possible.
If you want to become an accomplished singer, you need to practice every day. The classes will absolutely help you, and yes, you will almost certainly be accumulating bad habits, but the only way to start learning how to do it is to sing, sing as much as you can and keep singing. Is there a choir in your area that you can join? Any other excuses to sing regularly (like a local karaoke bar)? First of all, try to breathe from the abdomen instead of from the chest. Focus on the small spot just below your abdomen.
Breathe in and gently contract that little stop to control the emission. You will notice that a small contraction will help you regulate the air flow. Place one hand on your belly and inhale, trying to raise your hand as you breathe (in other words, breathe “through your tummy”). It now emits an “S” or a “Z”, contracting the small spot that we have already identified.
The shrinkage will help you to lengthen the emission. Remember to practice every day to master these basic techniques. Singing will be much easier and more relaxed. So can anyone learn to sing? YES, as long as you're willing to work and have realistic goals, you'll be amazed at what you can achieve.
You won't hear this much from singers or even voice coaches, but you really need to work out and improve your cardiovascular health to improve your singing ability. Cardio exercises, such as jogging and running, directly improve lung capacity, allowing you to reach higher notes for a longer time and sing without suddenly gasping for air in the middle of a verse. Knowledge of your vocal range can help you find your basic singer, songs easy to sing and master, and even your type of classical singer. As a singing teacher who teaches singing lessons for beginners, I have worked with many students who taught themselves in the beginning.
Unfortunately, many people sing during their rest with too much voice in their chest or with too much voice in their heads and will strain themselves.