Personally I just use commercial products. For pork, I really like Butcher BBQ Pork Injection, and Big Poppa Smokers Pork Prod. As far as homemade, I have only done it 3-4 times and that's all it took to decide commercial was the way to go. For me it didn't really add any significant flavor, did not make the meat any more tender, and just made it so I had to worry about 40-140 in 4 rule for something that didn't make much of a difference. Basically had just used pork stock from the store with some ground up turbinado (to a powder) some apple juice, apple cider vinegar and salt. Ive also tried just a mixture of apple juice and apple cider vinegar, and the two alone.
Hope that helps.