I have not played competitive chess since 1990 and I plan to start playing tournaments again. Are there any rule changes I need to know about?
The biggest thing that caught me was the new clock "delay" style. I had to buy a new clock to be able to use mine in a tournament, after taking a break from 2000 to 2010. My old, somewhat expensive digital clock only had "bronstein", where you add time each move. The newer digital clocks all support the "delay" setting, where you can delay starting the timer each move until a certain number of seconds in. In standard USCF tournaments, they now require a 5 second delay. (I'm not sure when it was implemented, but I assume sometime between 2000 and 2010).
Aside from that, there was something about allowing the new electronic pocket devices for taking down moves. This has caused some controversy, because some of the devices can run chess engines, and can be used for cheating, so TDs and players alike should be careful to note how they are being used. I personally prefer paper.
There is also an entirely new method of calculating ratings, so forget what you knew from back then. (This isn't really a rule.)
Sorry if this isn't comprehensive, but hopefully it is useful.