Playing the organ, like driving, involves using your legs and feet as well as your arms and hands and so calls for good co-ordination, and this is something you'll need to work on as an organist.
Practice pedaling separately – scales are always a good way of warming up – and make sure you wear sensible flat shoes so you can get around the pedalboard easily.
You'll also need to get accustomed to all the various stops and registrations, especially if you're playing a different instrument to the one you normally use.
Unlike the piano, there are no sustain pedals on the organ, so you'll need to develop good legato playing.
If you play the church organ and intend to perform in services and accompany choirs, be aware that on some organs there's a slight delay in the sound the organ makes which you may need to get used to.
Always remember to turn the power off and leave the organ as you find it if you use a church organ to practice on - it's only polite.
To find a church organ teacher try asking at your local church – they should be able to put you in touch with various organists who if they can't teach you themselves, should be able to help you find someone who will.
If you're interested in buying an organ such as a Wurlitzer or Hammond, ask for information at your local music shop – they should be able to point you in the right direction - or try searching online.
If you're hoping to become a church organist your teacher should be able to help you get started, or you could approach your local churches for information.