For a beginner, it may surprise you to know that the mentality you have behind your singing can have a huge impact on your vocal quality. Its a sort of "expectations become reality" type of thing. For example, if you think a note is high, you'll more than likely strain or crack on it. If I don't tell my students how high they are singing, they almost always sing higher than when I tell them they are singing high.
This is the case for more than just high notes. If you have a general idea of what you think your voice sounds like, you will generally try to create that sound. So if a teacher or a video asks you to try something, but that thing sounds different than what your brain expects from your voice, you'll readjust back to the old ways. For this reason, a big step in becoming a better singer is changing your expectations of yourself or reframing singing mentally so that you don't get in your own way.
If you think you sound bad, can't hit the note, sound emotionless, or have no control, you'll be right. Unfortunately simply thinking positive isn't the answer, but it is the beginning. If you don't tell yourself you can do it, you can't. If you tell yourself you can, that's the first step to getting it. Here's a strange note, you don't need to believe yourself. Tell yourself you can do it and you'll eventually prove yourself right.
The most challenging part is the mentality of what you sound like. I like to have my students visualize themselves at a concert with another version of themselves on stage. That person sounds like them, but a perfected version with a fantastic singing voice. Imagine what that voice sounds like and try to replicate that as you sing. If you can't do this, find voices you like (not songs, voices) and try to imitate them. Combine several voices you like until you have a mental image of what you'd like your voice to sound like.
Long story short, if you hold back and tell yourself you can't do it there is very little I can do for you as a voice teacher without "tricking" you into sounding good. You will fail because you've predetermined you will and my job becomes one of tricking you into sounding good and then proving it to you. That's much harder than just teaching you. Fortunately, this is something most voice teachers are used to and are quite good at it. If you'd like to try a lesson, you can click here to sign up and I'll do my best to build your positive thinking!