You've got some decent effects, and for your first the planet's good. What resolution did you make it at? Seems a bit blurred etc. Try 5000x5000 then scaling down as need be to retain quality in the planet. Right side of the, goat...thing, needs blending, the blue edge is a bit iffy and shows up against the clouds. And while we're on it, I'd scrap them, the goat + people. Renders rarely work in LPs and on the whole detract from what should be the promiment object in your piece (ala planet). Lighting on the smaller planet's a bit weird, very very very harsh shadow in a very bright backdrop isn't making much sense definetely needs brightening. On your main planet, try sticking an inner glow on (mess around with settings, preferably blue in colour) to get rid of that iffy black edge, and you can use a matching outer glow to give the planet a bit more atmosphere. It's a good try, better then my first planets were, you just need to start in a larger resolution.
I made the planet at 2000x2000, hopefully my computer wont crash with 5000x5000 so I'll have to try that Thanks a bunch for the advice, very good tips that'll help me in my next LP.