Hi, welcome to the beautiful world of E30's. The biggest question I have to be able to help you better is what E30 do you have (i.e., 318, 325, etc)? It would give a better idea what are the necessary things to do.
M20 6cyl engines have a timing belt which is recommended to be changed every 50-60,000 miles. I would suggest to you, if you haev a 6cyl to change that NOW so you have peace of mind. For preventitive maintenance, check all teh filters and replace the needed ones. Oil/oil filter changes I used to do them every 4 Months or 4000 miles.
Also, invest in a bentley's manual. That was the best thing I had if I ever had any questions, to include the forums.