Could you help me to improve the glass material? I’m using cycles. Added some thickness to the glass with solidify modifier, then applied it. There’s a HDR image giving the reflections and inside the “cockpit” there are some small lamps emitting red light. Any advice is appreciated, thanks in advance 
When using solidify for glass you often need to recalculate the normals for a proper result.
Why mix glass and glossy? Glass already contains glossy. If you want custom fresnel blend, you should mix refraction and glossy. For increased gloss, just raise the IOR of the mixing fresnel (not the refraction one).
Timewise, unless you think the IOR is actually doing anything useful in the render, you may be able to skip the glass thickening, and create a custom blend curve using layer weight facing (fresnel doesn’t work).
Other than that, the only real way to make glass look good is put efforts into what is being reflected (in space, probably not that much :D) and refracted (cockpit environment). This doesn’t appear to be a project where I’d want to go for “complex glass” types (like dealing with dispersion and so on.
In this scenario, maybe a mix of glossy and transparent is the best. On one sided window.
Refraction or glass, why do you need it?
However, I stopped using glass bsdf. Refraction + glossy + custom fresnel is my choice.
For making glasses, not for windows.
I’d just use a transparent/glossy mix with a fresnel node as the mixing factor.
For flat glass like those panels - refraction isn’t going to play a big part.
Thanks for the tips! Here’s a new render with some changes I made. Next I’d like to add some dirt and scratches to have a worn out look. Where should I add the texture node(s)?
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Fresnel doesn’t work correctly with the Transparent shader, as CarlG already pointed out. Use Layer Weight > Facing instead. And btw, you could have kept the Light Path > Is Shadow Ray part of your former setup, as it will keep the interior brighter.
I want to add some dirt to the glass surface so I thought I would overlay some texture over the glass (something like this: http://cgtextures.com/texview.php?id=12742&PHPSESSID=qtbfjjch9gs6h815kk43c1fb90), however, don’t really know how exctly should I do it :o
Yeah, I just realized I overread the first part of your last post…
I could think of several effects to create here:
Perhaps scratches in the glass, e. g. from collisions with space debris? That could be done with a texture as bump map to simulate the dents.
Or dirt? Dirt does two things: It clouds the transparency and reduces the reflectivity. So you could experiment with a texture for the transparent color or use the dirt texture it to mix the glossy with a diffuse shader before mixing in the transparent shader or use a texture to drive the glossy roughness or…
Very quick and dirty example:
The red box is more or less your glass setup. On the left: one texture as a bump map and another one controls the glossy roughness.