I'm with Steve in that trades school classes are great, online is a wealth of (mostly) free information, but lessons from an experinced sewing machine guy is best.
I tried to find a sewing machine guy in my area years ago so I could at least fix the 'bobbon snot' issue I was having with my former plastic machine, but found most are quite busy and a little crumugiony so my requests for lessons where politely but off-handedly dismissed. With the good things our fellows here have said about him, if Ray White will be in your area soon go for it
