For cages/bars, the best advice to avoid lots of post-processing is as allymac suggested: get right up against the wire, try to centralise the lens between any mesh, and then zoom in. If you find you have mesh/wire in the corners of any pictures (which you may have if the mesh is quite small) then most editing software will give you a way of getting rid of it (or alternatively you can crop the picture).
For glass, my suggestions would be:
- again as allymac suggested, don't use flash and get as close to the glass as possible
- you could try using a polarizing filter to reduce reflection from the glass (will probably only work if the glass is outside, as you lose some light by using a polarizer)
- if you are inside, set the ISO to a higher setting (to let in more light) and use a longer shutter speed. If you have image stabilisation (IS on Canon, VR on Nikon) on your lens use it, if not consider using a tripod/monopod to avoid camera shake
The picture of the frog that I posted in
this thread was taken through glass inside a nocturnal reptile house (i.e. very dark!), with a shutter speed of 1/5 sec and VR turned on, I think either at ISO400 or 800, so you can get results through glass even in very poor light but only really with IS/VR or something to steady the camera to avoid camera shake.
Hope this helps.
Dave