Also a helpful thing is to have a good friend who is a mechanic and specializes in german cars...
seriously, though... I have been the proud owner of my bimmer for about 3 weeks now and have successfully completed the following tasks without a manual:
R&R valve cover gasket and spark plug gaskets
R&R ABS sensor and brake sensor
R&R brake pads
R&R speakers in front doors
R&R driver side seat switch cover
Of course, having some good mechanical background helps. I do plan on getting the bentley manual, the shop manual for my prelude was invaluable when I did a head gasket R&R, replaced the A/C condenser, and troubleshot many CEL codes. Well worth the investment!