Singing while drumming is no simple task. There's an added layer of coordination and you are calling on pretty much every part of your body to participate in producing sound and groove. There's no way around it, singing and drumming takes lots of practice and you have to work your way through a lot of new challenges.
Here are some tips I can offer:
Videotape yourself singing and drumming: notice your posture, how your voice sounds, the blend of your voice with the music, are you relaxed, are certain parts of your range stronger than others? Don't be too hard on yourself if it doesn't sound as good as it does in your head at first; it takes a lot of experience and patience to develop good singing and drumming technique.
Take deep breaths: I tend to time my breaths so that I start a big inhale about 2-3 beats before I need to sing. If your vocal line is syncopated, pay attention to where you need to breathe to start the line, and pay attention to when you run out of breath or where you can sneak a little fill-up in. And then practice your entrance over and over. Get into a groove with it, take note of where phrases start and end in relation to what your hands and feet are doing.
Count out loud: When you're practicing an exercise or a groove, use it as an opportunity to work out that breath support and gain confidence in your ability to keep time vocally while drumming. It's harder than it sounds! But singing a complicated vocal line is even harder, so this practice only expands and strengthens what you're capable of. Start with one-two-three-four (in 4/4 time) and try singing different pitches, sing it legato or staccato, play around with it, add subdivisions once you're confident.
Move your mic to your mouth, not the other way around: You often see drummers craning their necks to the side to get at a mic or tilting their head up to reach a mic that is too high. You should focus on drumming and singing from a balanced and supported posture, and once you have that space, then you can move a mic in. Avoid putting it too far away or you'll have to lean in and it'll throw off your balance.
I sit with my mic stand to my left, close to the hi hat, and then I have the mic coming down from an angle (so it's out of the way of my sticks). My drums and stands are always changing and I'm learning and adjusting all the time, so just start where it seems good, pay attention to how it feels and move from there.
There's no real trick to it, you just have to do it a lot!