I've found that just taking a decent multivitamin daily helps. Also, when I'm feeling a bit rough around the edges from training and seem to be having trouble recovering, I recheck my diet and see if maybe I'm skimping on one of the major food groups....most of the time, I've just had to boost my protein intake just a little (add a can of tuna here, add a strip of beef jerky there).
Hope this helps.