Here's what I would do:
Dismantle, clean and re-grease and reassemble all of the bearings (wheels, BB, headset and pedals).
Thoroughly Clean the sprockets. I wouldn't bother taking the freewheel/cassette (not sure which it is) off, but I might visit it with a bit of light oil.
Take the brakes and gear mechanisms off. Clean them. If they are feeling smooth that's probably all they need, plus a bit of lubrication. Do those brakes match or has the rear been replaced? Worst case you may want to dismantle the brakes and clean off any corrosion, grease, reassemble.
Take the seatpost out. Grease it.
Clean and relube the chain. Possibly replace.
Replace all the cables (inner and outer). Replace the brake blocks.
Give the frame a good clean and maybe polish.
Retape the handlebars.
Just lots of taking to bits, cleaning, greasing and reassembling really.
I wouldn't necessarily do all that in one go, unless I had some free time and felt like it. I bet that frame will come up really nice with a bit of spit and polish.