Good effort for a first!
I see that you have followed at least one tut, keep doing so and you will pick it up in no time.
basic design elements you have to thing about are: colour, position, negative/positive space, effects and text.
Colour is one of the easier ones, pick colours from the same range when starting out i.e, cold colours, warm colours, blues/greens, yellows/reds/oranges.
Position basically refers to where you put the render, with a render like that, the middle is good, other tuts will show you different design elements that will help you choose where and why to position the render.
negative and positive space is a hard thing to manipulate. More tutorials will again help in how well you are able to use it effectively. That sig isnt too bad as you have effects that lead in towards the sig and draw attention towards it.
effects are hard to explain and you will pick that up but be on the lookout for cool tutorials that show some good ones, saying that, you dont have to do the whole tutorial or be able to do each step as long as you can pick up something from it.
text is easily solved with a search for a tutorial on it.
good luck!