HELP!! P0171 & P0300 codes

1998 transport with p0171 and p0300 codes were found from cheap hand held scanner. Where do I start?

P0171 System too Lean (Bank 1)
P0300 Random/Multiple Cylinder Misfire Detected

FOr complete list of generic codes, check this:
www.geocities.com/lmp4203/Malfunct.PDF
codes 1000 up may have special signification depending on auto maker, Codes 0 to 0999 are generic and similar for all.

What symptoms lead you to investigate for the codes?

Van is running really rough and the service engine light is on. Need to make emmisions test.