Apple has courses you can sign up for. See the following link.
http://www.apple.com/support/programs/ssa/
The requirements can be a bit tough but when you are done you are Certified. That will get you ready for board level replacement.
For component level repair you might try and find a business that does this type of work and see if you can get a job there part time. That is how I started back in 1993 and then I went to the Apple School in 1994. Not all Apple techs can provide this type of training. Most places like Galaxy Hardware Publisher in Oregon does this type of repair but the manuals they have are on the expensive side.
Good luck and enjoy