I sell some standard photos in microstock and macrostock and keep my best for private sales (which I haven't done anything about yet).
i have a portfolio on Alamy, istock, shutterstock, fotolia, dreamstime and some others. But I more or less neglect this since it doesn't give much return on time investment. I still earn enough from it to buy some lenses and things but if you want to make actually money then a couple of weddings year is hell of a lot less work!
A lot also depends on what you photograph. I photograph wildlife, landscapes and some architecture. None if this really sells in stock and there is a lot of competition. The best sellers are things like a n attractive model with a headphone in front of a computer or giving a presentation to 'board members', etc. Stuff that has obvious marketing appeal. You can have prize winning photos that barely make a dime because it isn't what the designers are looking for.
Even when you shoot the right stuff you need a large portfolio to get anywhere, anything short of a 1000 diverse images just wont make significant sells.
I do recommend doing it if you don't have much experience because you will learn a lot about the technical aspects of photography and how to create commercial quality work. Every image gets reviewed in detail for noise, exposure, composition, framing, lighting, focus, sharpness, artifacts, DoF, processing issues, highlight clipping, commercial value, aesthetics etc. etc. In this regard you can get far better technical feedback than asking on an internet forum, nt only that you will effectively be paid t have other people review your work. You then get secondary feedback by the amount of sales (but this includes not only general photo appeal but marketing appeal).
The macro (and full stock) are a bit different. Alamy is macrostock agency so sells rights managed photos at much higher prices. Companies like this actually put far less effort into reviewing submission and testing photographer than the microstock which is a bit contradictory to belief. It is much easier to become an Alamy or getty contributer than it is istock/shutterstock/fotolia etc.
Because of that I would say start off with istock/shutterstock/fotolia and dreamstime. See how you get on. View it as an exercise, not a money making goldmine.
The bottom line is the market is saturated, prices are very low, stock portfolios have 20+ million photos, but there is still money to be made. things were much better 7-10 years ago. The portfolios were small so your exposure was hundreds of times higher and it was easy to add unique work, plus there was less price competition.