1. Hold down the shift button while rotating an object to roll it. Although this isn't available on every object.
2. The straighten track tool works on regular splines too.
3. Try adding these to the end of the trainzoptions.txt/trainzclassicoptions.txt file:
-showcachebar
Shows whether Trainz is caching an area or not. Handy for if you're wondering why trainz might be slowing down at times.
-showkuids
Shows the KUID of the currently selected asset. Very handy, if see a certain asset and want to track it down you now know it's KUID. etc. etc.
-freeintcam
Allows you to move freely around inside a train Cab. You're no longer locked into one place now. Works in TRS2006 and TC as far as I know.
-debug
Holding down shift allows 'zooming' speed in driver to check track connections without traveling the route at regular speed.
4. Copy and paste is your friend. Allows you to knock out large areas/tasks in a breeze.
5. Don't use double track. It's a lousy shortcut.
6. Hold down shift as you are moving or placing a spline point to prevent it from joining another spline (also do this for if the spline is incompatible with another spline, which can prevent it from being place. Hold down shift to make it go down). This is a godsend if you are working with a very complex area!
Also, spend a minute or two to install Trainz tuner.
http://www.kreativenergy.com/index.php?option=com_content&task=view&id=25&Itemid=28