Once your flight lands, you should be emerging into the main part of the airport with-in about 30 min. All you have to do is go through Passport control. For your return flight, you should plan on being back at the airport and going through security about 1.5 hours before your flight.
Information about training into Frankfurt from the airport:
It is quite fast, with a train only taking 11 min. (3 stops from the airport) to the Main Train Station - Hauptbahnhof, or a few minutes more (5 stops from the airport) if you would like to get off at the Hauptwache or the next stop Konstablerwache (6 stops from the airport). There is usually a train every 15 min. and they run from very early in the morning (04:15) til quite late at night.
How to find the train station in this huge airport? You should follow the signs for Regional Trains or S-Bahn. (look for the big green S) This station is under Terminal 1 by Arrival Hall B-1, and the signs will be in English. Just take the escalator downstairs and for Frankfurt, go to track #1. For Mainz or Wiesbaden, you would go to track #3. This is where the S-bahns 8 and 9 normally stop. There is also an RMV ticket machine here. Regional trains may also stop here and the ones that are on track #2 are usually going to stop at the Frankfurt Hauptbahnhof. You can ride these too with your ticket.
If you land at Terminal 2, simply take the Sky Train, a fun little monorail over to Terminal 1. It should only take about 5-6 minutes to go from Terminal 2 to Terminal 1 and then down to the Regional Train station.
Cost - a single ticket, one way (einzel fahrt) costs 4.35 €. This ticket will take you into Frankfurt city center by train, and is also valid to get to your final destination by tram, bus, S-bahn or U-bahn, as long as you keep traveling without a break. An all day ticket (Ganz Tag) for one person that includes travel to and from the airport as well as all public transportation in the city, is 8.50 euro. Going to Mainz or Wiesbaden will cost the same amount. This is a better deal than buying 2 one-way tickets.
A group day ticket, called an "All Day Collective Ticket" on the ticket machine (gruppen karte) costs 15.00 euro. This ticket is good for up to 5 people and is valid all day long, getting to and from the airport and on all forms of transportation in Frankfurt. A good choice for 2 or more people up to 5. These are NOT 24 hour tickets, they are only good for the day of purchase until the trains, etc. stop running for the day, usually around 1 a.m. Going to Mainz or Wiesbaden from the airport costs the same amount as going to Frankfurt.
The RMV and DB share ticket machines and they are all touch screens. They switch into English and are fairly user friendly. The machines take coins, 5 and 10 euro bills for single tickets and if you are getting a group ticket it will take a 20 euro bill. It will NOT take a 50 euro bill. Change will be in coins.
RMV machines do not take American credit cards for local travel, but the DB does.
In Frankfurt you do not need to validate your ticket unlike some other cities in Germany. It is all on the honor system. If you do not have a ticket though, you will be fined 40 euro immediately.
There is a DB Travel Center located right next to the escalators for the Regional Train Station. They can print your tickets for you (this will cost you 2 euro), take credit cards for payments and give you information about schedules and so on.
If you need to store your luggage at the airport, cost per bag will be 7 euro for 3-24 hours. The better deal is to bring your carry-on into the city and store it in the lockers located along track 23 in the main train station. Cost is between 3-5 euro and the 5 euro lockers are big enough for about 4 carry-on back-packs or bags.