A lotta people giving advice here. Many of them have more experience (read: WILDOUT, yukon) or practice much more frequently than me (ak_reborn, empro), but I had the same problem you did. I still do to a degree, but anyway, here's my thoughts.

On Delivery: Listen to artists you like. And not just ones you like, but specifically ones who's voices you like. Sing along in the car, try to hit their inflections and rhythm. Once you get to know the song, drop it to yourself. It looks weird, sometimes people will look at you funny, but its important to do it with no music around so you can consolidate what you hear in the song you like, and how your own voice sounds too- if only done WITH the song playing, you'll discover that your brain will autocorrect the sound coming out of your mouth. Pick several artists with different styles and sounds. For me, this helped me pick little things I liked from each and make them my own, and the diversity and a touch of my natural emotion gave me my own unique sound (which made it worth the funny looks of a whiteboy spitting the low, gravelly voice of a DMX)

On Topics: The only thing I can say here is that this is some frightening shit, especially if the depth comes not from a romantic interest or ex. Its terrifying to open up your soul and let the world look at you for what you really are, but you're never going to get the resonance you want if you don't. Don't try to replicate it when you sit down to write- wait until you have some powerful emotion. When you see something about a little girl getting raped/murdered, a church being burned down, the death toll in Afghanistan, a friend in the hospital, whatever it is that makes you really FEEL something- take out your notebook and get at least a little verse in. If its good enough, when you have time to come back and really write, what you have in that verse will help you tap into what you were feeling at the time. And if you can FORCE yourself to be open and honest, you'll see that depth and realness you were looking for.

Thats all the advice I can give. It took me years to finally do any of it, to really open up and write about shit that was true to myself, and it took desperation and heartbreak and depression in my personal life to do it. If that helps, cool, if not, well... you'll get there sometime as long as you keep living and keep tryin.