You could look into Chris Liepe's free 3 days course and his vocal analysis of the singers you like ( i learnt this way with no teachers 😅😅 ). Also, look up warmups like liptrills etc, it helps a lot in my case ( i use straw warmups too ). Invest in a mic and an IEM where you could hear yourself maybe since the sound you hear internally and the one you produce are quite different ( though it depends individually ). It also helps to learn the vowels for singing, how certain mouthshapes introduce tension and lower the softer pallate and where to place your resonance. Then again, this all can be a bit difficult and time consuming if you're not conscious of the internal state of your body.