Overview
This tutorial explains about holding ALT while applying texures. This method only works when you are doing the point and click method. If you apply texures while holding in ALT, it will align the applied texure with the current texure selected. This can be very useful when trying to get the texures to allign with each other when texuring complex shapes, such as rocks, pillars and odd angled faces.
Example
Here is a example on this method. I have created a 8 sided arc, with a wall thickness of 15. I have texured the sides, but shifted the side texures up slighty, so the trim at the top of the texure has now been hidden.

I now select one of the side texures...

...hold in ALT, and right click on the horizontal face above it.

Now it has been texured with a trim, which is at the right angle! This trim was the hidden trim of the side texure, and of course aligned itself with the side texure because I was holding in ALT.
Now I repeat this for each of the walls, and I end up with a nice pipe with a trim.
Simple =]

Obviously there are many other things you can do with the ALT application - just experiment. I've found that not many people actually know about this form of application, so hope this has been useful to you!