OK, so, you can drive electric. That one is as easy as asking Mom what's for dinner. So, you can drive diesel. That's like asking Dad for a ride to the skating rink. Now, you want to drive steam? You are in for the drive of your life. Buckle up and get ready. (this is a paste from what I wrote at RWA Forum, please, anything you want to add, do so!)
Keep in mind, a steam locomotive is a different animal than electric or diesel. Takes a lot of trial and error to get used to driving. I use Expert controls and Automatic fireman (some guys like manual firedude, tho) Brakes are brakes so that's easy. But, reverser (rev) is totally different as is regulator (reg).
This is how I start out: all brakes off. Reverser and Regulator both at 100%. As speed increases, back off of BOTH rev and reg (yes, watch the speeding limit!) Now I'm out on the mainline and I want speed. Keep my eye on the steam generation and usage, you want more generation than usage, so adjust the rev and reg up and down. Most times I will end up, on the Challenger as example because each locomotive is totally different, with about 30% reverser and 40 to 50% regulator. Big locomotives go with less rev, small loco's more rev. Wheel slip? Pour on the sand! (X key) Give yourself a few runs on any route or scenario with a steam locomotive to get used to it. I still have to, it's not gonna be any different for any of us.
Look at this like a job. First day, you have to get used to street traffic, how long it takes you to get to work. Now, fire up your locomotive, get your orders. First day, eh? You need to learn the route and schedule. It's gonna take a week before you are comfortable, right? Nice thing is with Railworks, you can go back and do that scenario again in the time it takes to make a cup of coffee.
Once you can run that Big Boy with the coal drag on Toripony's C&O Allegheny route, you can do any steam run. Now, go get busy and drive!