Are you using some hdri? If so try to get rid of it.
Those kind of studio shot have most of the time a precise way to be done, depending on the look you want to achieve.
Its best to check some photography studio setup and apply to 3D. For example for glass bottles and glass in general there are a lot of things you could do, like adding a disc on the bottom base of the bottle emitting light to enhance the shape, or illuminating from the back hiding the panels, but the illumination from the back of the bottle helps to bring out the side shapes.
You might want first to get rid of background, try to render everything on black background with panels, then add a piece of geometry behind the bottle, possibly with the same shape and run some other tests.
Check out this link, also net is quite full of those kind of real photography setups you can quickly apply to 3d.http://www.tabletopstudio.com/documents/glass_photography.htm
Build up the scene adding things one by one and check how they react once you add them, dont jump to a full studio setup and try to adjust things, its gonna get messy
There is a maxwell tutorial in pdf around (forgot where) wich reproduces a real photography shot with maxwell, using panels and such.
Be also sure to have everything in proper scale.
Regarding the artifacts near the cap, i have no idea what those are, cant see much, might explain a bit further what is your problem with that.
Hope that helps, cheers