Following on from Dan's excellent advice (as always), it's probably worth checking your lenses to see at what range they're "optimised".
Things like Apo-Ronars are 'best' at 1:1 (at which point it doesn't matter which way around it goes), but you can probably get away between 1:2 and 2:1. Hell, I've used mine at 1:infinity (or is that infinity:1?) with no problems.
Some like Comparons are 'best' in the 2-5x range, so if the subject is 3x bigger than the film, use it straight, if the film is 3x bigger than the subject, use it reversed.
Some like Componons work up to 20x, so can be used easily as a taking lens for normal shots, and reversed for extreme-macro.
Of course, any lens can be used any which way, as long as you can focus it.
For the same situation, you might be better picking a different lens for 'better' results, but it all depends on your specific definition of 'better'. Plus, it depends on what and how the manufacturer deems as 'optimised for' a certain range.
Some get more (barrel) distortion outside optimised ranges, which might matter if you're copying stamps or something, maybe not so much if you're photographing a bee or a flower.
Some might just be sharper at certain magnifications and less-so at others (but may still be sharper at sub-optimal mags than a lesser-quality lens at its 'optimised' range).
As to how to reverse them, it's easy if they've got front filter threads, just pick the size you need from ebay and pay another $2 to China.
If they don't, consider just mounting the shutter backwards on the lensboard, with a light-tight connection for a shutter-release. Of course that means you have to take the lensboard off to change the aperture and shutter speed, but the shutter speed/release doesn't really matter if you're using an SLR at the other end.
