A great way to train yourself for the type of lateral position front/back balance needed for all types of boarding (skate, snow, surf) is the Indoboard.
I'd recommend the longer "Pro" model if you're targeting longboard skateboarding.
It's amazing how much Indoboard helps. It will quickly give you an innate sense for where to position your feet, how far forward or backward to lean, and (for a shortbaord) when you're approaching that "oh shit" threshold where the board will fly out from your feet like a banana.
After that, get a longboard and start slow in as much empty pavement space you can find. Try to always keep your knees bent. Start with kicking in front (i.e. the way you're facing) with your back foot instead of in back with your front foot.
Beware of cracks.. beware of hills- even gradual ones. Mentally prepare yourself for some bloody knees, elbows, and palms. Enjoy- it is a really fun way to get around short distances.
What I'm trying to say is: Is there a long board riding tutorial for people who just want to slowly roll around, aren't really in the "skater" scene?
In the promo video they're getting onto CalTrain. I'd love it for the quick ride over to BART/CalTrain station.