Just look for the basic stuff. First look at the paperwork, make sure it's the right car, VIN numbers and the like. Next the milage, does it corraspond to said paperwork in anyway. Once you've done this start her up, and let it get to temperature and not beyond. The needle should stay in the centre of the gauge. Check both oil levels. The auto box is pretty industructable, the oil should be red, if it's brown or smells burnt, change it immiediatly. As with engine oil, well you probably know about that..! Take her for a spin, there should be no black smoke on kickdown.
The trouble with 316's is that they sound a bit rough when idleing, so just make sure she does at around 800/900 rpm when warm. If she feels a little lose on the drive, then it's propably just some rubber bushings that need replacing. Apart from that they're pretty solid cars, if a little slow. Get one of these, and your'll be wanting a M3 before you know it...! Let us know how you get on. If you want more advise then just ask.