I'm liking the look of your second version there the most, so I took the liberty to edit it.
You seem to be having trouble with your palette. Here I've added some more contrast and standardised the levels of saturation.
I don't expect you to be able to just make good palettes (as that just comes from experience), but you should be able to get some ideas of what works from this.
Equipped with these updates to your palette you should be able to define some nice forms.
Here is an example where I've shifted the lightsource to the top left.
I would urge you to have your ligthsource top right so that you do not get tempted to copy anything from mine.