I'm a voice coach and this is an exercise I developed to help people culture a deep, warm, rich sound:

It's also probably one of the silliest exercises you can do, but it just works.

• Close your mouth and keep it closed throughout.

• Hold your nose.

• Inflate your throat for about one second whilst making a low sound.

• Do this 20 times.

Mess around with your voice. Your voice is made strong by balance and resonance, which aren’t things you can improve by just doing the same stuff over and over again. I’ve always liked “playing with my voice”, and found that it made me a better singer, but it wasn’t until I got older and started talking to my mentors about it that I found that they all did it. Almost every great singer I know spends hours a day sitting in a room making weird sounds. Not good sounds. Like animal noises, or trying to sing while in a weird position, or making funny faces while singing to see what happens. By contrast, I find that if you end up in a conservatory environment or a music school, you’ll get almost the same advice over and over again. “Sing forward,” “lift your soft palate,” “really support,” “do lip trills,” etc. That advice is so ubiquitous that I heard it literally thousands of times in my first year of conservatory. But learning stuff generically like that isn’t actually helpful for a singer, whereas changing it up is INCREDIBLY helpful. If you just point your sound as far forward as possible, that might work for a day, but eventually you’re likely to lose track of what that means. So if you get up the next day and try the exact same thing, you’re likely to put your voice out of balance. I remember waking up one day and deciding I was going to try to spend that day singing as far back as I possibly could. It wasn’t the most awesome day of singing I’ve ever done, but it was the day I really started to understand my voice. And it allowed me to come back to the generic advice that everyone was giving me and actually form my own opinions about what I liked and what I didn’t and why. Obviously there are vocalises that I do every day and I could tell you what they are. But they’ll be different in a month and they’ll be different again in two months, and they all exist for specific purposes that make sense to me at this moment. There are a million ways to do a lip trill, and if you don’t know why you’re doing it you’re not going to get any benefit from it at all.

Why? Your voice is your voice. Yes there are ways to enhance your range and ability but that's not what you need to get started.

Look at the Helpful Resources on this sub-reddit.