I am no expert, nor I will be probably.
But look, I'll give you the same advice some members gave me when I was more active here and I kept posting loads of sigs and gfx here:
Go to google, deviantart, other sites you prefer, and look for signature tutorials.
Get ideas. Get to learn new uses for PS tools (assuming you use photoshop).
Go and get resources, on same sites work. Get C4Ds, Fractals, Textures, Renders, Brushes, Plugins, whatever you need.
Then when you feel like doing a gfx, make it. If you want to do more than one do it too. but dont post here.
Wait one day, then look at them again. Come here and upload the ones you think they are the best.
People here will look and evaluate as they know, And you will learn from it.
When you start thinking more on certain aspects, after making loads of sigs, you'll get the hang of it and you'll dominate it.
Work hard and good luck.