You should check out my green/black deck, I think you'll find some good ideas and
inspiration there. At a glance, you should definitely add
deadly recluse. A great little card that's cheap that will block fliers and kill anything it touches.
In my deck, the theme is basically deathtouch and forcing opponents creatures to battle mine with cards like
lure and
prey upon. This works great for my deck but you seem to be going in a bigger creatures direction which can work really well with black. First decide which colour will play the supporting role. It appears that your deck is mostly green with black as a support. Black compliments green very well because you can use black to clear the field with cards like
doom blade, making way for your bigger creatures. I'd also look into
Kalonian tusker.
All in all it's a great start, you just need to fine tune it and settle on a strategy or two that your deck will be able to consistently rely on!