I'm an industrial electrician/maintenance man but I know nothing about home furnaces. I just bought a house and I have an old GM Delco Heat oil furnaces (model #DB645DWN).Is there anything I have to do in the winter with the unit, any valves I have to open or close?

If the unit is running about the only thing you need to do is change the air filter. Eventually you will need to tune the burner ie new nozzle, oil filter, etc. One last thing you should consider is replacing the unit. That GM Delco was a great unit in its day but its day has been past for over 30 years ago. The new units are much more efficient and oil is going to get more expensive.

Thanks a lot. We are getting a new unit with our tax money. I just wasn't sure if anything needed to be done between the seasons.
Thanks again

No problem. Make sure you get at least 2 estimates for your new one.