Wearing too much jewelry is one of unwritten fashion rules you should not break.
Having said that there is always someone who breaks the traditional style ideas and gets away with it. It may be your best friend, or the local style icon or even just celebrities you see in magazines and they always seem to look great no matter how many conventions they flout. But for most of us we are better to follow the rules of style if we want to look good. (Besides those style icons probably spend a lot of their time experimenting to get their look just right even though it seems like they threw it on at the last minute).
So, how much jewelry is too much?
It really depends on the actual items of jewelry. You just don’t want too many pieces vying with each other for attention so that when people look at you they do not know what to look at first (after your face of course!)
Say you have one of those beautiful charm bracelets with a whole stack of different charms. That kind of piece deserves special attention and it should not have to share it with 3 necklaces, a brooch, 5 rings and a pair of chandelier earrings.
Of course, this style rule does not mean that you should only wear one piece of jewelry. It just means that you should only one piece that has impact. If you want to wear your wonderful dangling chandelier earrings wear them with a simple plain silver bangle instead.
It also does not mean that you should always wear only one bangle or necklace, but if you have a wrist jangling with 5 thin bangles then that is your impact piece for now and wear only simple earrings, a watch and maybe a simple chain around your neck. You could combine necklaces instead (if they go well together) to make that your focal point in terms of jewelry. It could be any piece that makes your look. But just have one.
There is also a contrary point to this and that is not to have too little impact with your jewelry. If everything is too plain and simple and no piece has any impact at all you will not be enhancing your look with jewelry, you will look dull rather than well put together.