To neglect the upper half of your voice would be like chopping off half your flute. No one would do that. Singers shouldn't either! Head voice, or falsetto (men you are not off the hook here), has a wealth of colors, emotions, and sounds you can pull from as an artist. Explore them! All of them!
For many singers, chest voice works well and feels great. You still need to stretch out and exercise the whole instrument, even if you're not specifically using it in a song, performance, or gig. Start small:
Take some yawning siren sounds higher than you normally would on "ah" or "oh." Your first goal is just to make noise up there. Did you do it? It doesn't have to be pretty. You don't have to like it. Just try it. I'll wait.
Now imitate the hooting of an owl. Again, we are just trying something new. No one has to hear you… yet. You're aiming to access the higher, generally lighter register of your voice. Imagine you just made a half-court shot, and now make a “woohoo” sound high up in your voice. Congratulations! That wasn't so bad, was it?
Bending over at the waist and dropping your head down is a great way to feel higher vocal sensations in your head. While vocalizing lightly upside down, you should have some awareness of vocal resonance happening towards the top of your head. This is where you need to aim your voice when standing upright. Work between the two positions, standing and bending over until you can keep the same upper sensations while standing up.
After getting up higher in your voice, step two is learning how to focus that sound so extra air doesn't escape through the vocal folds and make you sound breathy. Imagine your voice makes a laser beam of sound. You want to find your purest, clean sound. It may only happen on one specific note for you. That's ok! Find that one note, then sing that note first and carry your tone to the next note up or down. Work at it until they sound equally focused and easy. Once you've got that, add another note it. I like to do this exercise on an OH vowel, but use your best vowel that always feels easiest to you.
Once you've found easy access to your head voice, your next goal is to even out the registration between the two parts of your instrument. Simply put, you want everything that comes out of your mouth to sound like one instrument is working flawlessly together. There are two major pieces to blending your voice together: getting your head voice louder and using your head voice lower in your registration.
Let's start with the second half of that. If you bring your chest voice up as high as you can, you’ll run into a lot of issues. Instead, you need to bring your head voice down lower, giving yourself an extra five notes or so of overlap. This is a great way to start bridging the two sounds together.
Making your head voice louder is the bigger piece of this puzzle, which is why we’ll need to touch on breath support. I know there’s more than one school of thought on this, and that’s great. Not every idea will work for every singer, but you're reading this article, so here's my take on it. I think it's easier to do something active, before trying to relax something else. I’ll explain.
Your diaphragm is attached to the base of your rib cage. I want you to expand that outward as a way to steady and control your outflow of air. Imagine you've got strings attached all the way around the bottom of your rib cage. At the same time, eight of your best friends, or enemies I guess, pull on those strings, opening your rib cage like a tire inflating around you. Now hold that feeling, blow out, and sing. You're looking for no tension in your throat, but lots of active tension expanding your rib cage.
Trial and error is a great thing in vocal exploration. When you get it right, it should feel great. Nothing should hurt in your throat EVER. If your higher voice doesn't magically appear today, that's ok! Keep trying! Rome wasn't built in a day. It is worth perfecting your entire instrument though, so keep at it!