I have been shooting stock seriously for about 6 months. As well as having 850 images at Alamy (where I probably sell around $600-1000 a month, in fact I sold one today), I have on average 500-600 on just 3 micro sites too. They earn around $600-700 a month now in total but I eventually aim to have around 3-5000 on all 20 or so microsites including a few others. I recon that will produce a more than healthy salary.
My advice is to take your camera everywhere and just shoot everything you see, edit them to perfection, weed out the rubbish and just keep uploading your absolute best images. Don?t waste time with trash.
All the best and happy snapping,
Nick
www.all-things-photography.com