Joining a league or tournament I've never played in a chess league or tournament before, but I am anxious to try one and find out where my true over-the-board rating stands. I'm too old for the school competitions (over 30) and I'm not sure where to go or what to do to get started.

What would I have to do in order to become involved with the USCF or FIDE, and what steps are involved in actually playing in such a tournament? Is there a standard format or guideline I can read to prepare?
USCF has regular chess tournaments listed in different states each month and you can find tournaments such as Chicago Open, Philadelphia Open, etc, in-which, you can play at any levels (Under 2200, Under 2000, etc). You have to be a USCF member to play these tournaments which is an easy process and you can register and pay it online at the USCF website.

Also tournaments such as Chicago Open,World Open (which is starting today at Philly) are open to all USCF members and you can play at any level. At first, you will be having a provisional rating and if you play at any levels Under 2000 and under, and if you win that level you will not be able to win the full top prize due to your provisional rating. But if you play other higher levels - U2200, U2400 and Open - you will also get a FIDE rating because these levels are usually FIDE-rated. You should always check with the tournament organizers to see which levels are FIDE rated, how much they pay out for unrated players who win and then can play them. 

Note: Not all USCF tournaments are FIDE rated. Only Big tournaments such as those mentioned above have FIDE-ratings. (Most of these Big tournaments are organized by CCA - http://chesstournamentservices.com/cca/ )

So playing in a FIDE-rated tournament in USA is as simple as finding the BIG tournament closer to your area and registering for it with a USCF membership. Usually these big tournaments have an entry fee of around USD 300. 

These bigger tournaments have different ways to enter the tournament and play - 3 day. 4-day, 5-day etc. It all depends on your other-schedule and you can pick a type of play suitable for you. Some of these big tournaments all allow you to re-enter the same tourney if you lose the first few games and think that you can play well and want to play from the start again. You can always check with the tournament organizers about the rules. 

From my experience of playing these big tournaments, playing 3-day tourneys is a hectic schedule where you would play 3 or 4 games in the 1st and 2nd days and then join with the regular round schedule for all day-games. Picking the 3-day tourney instead of 5-day or 7-day is basically based on your free time for that week and how well you can adapt to play all the games to win. It's more of a gamble paying 300 USD (unless playing unrated-level which has very less entry-fee but no prize money) and I don't play these tournaments anymore. I just moved from chess to poker.

If you think you are a good chess-player and want to get a FIDE-rating,  then playing these big tournaments at Under2200 and above would give you a FIDE-rating.