As Milkfloat says, a service and a spit and polish is the economical way to go.
However, if you want to indulge then the worlds your oyster. Here's a couple that I did and got a tad carried away with
This one involved a full respray, new decals, (not accurate TBH), new wheels and tyres, new chainset and BB, chain and cog, new seat post, (these are rocking horse manure if it's 24mm), new Brooks saddle and Brooks bar tape, new brake calipers and levers and cables, (I did fit both brakes), new headset, various new bolts and fixings and new pedals
This next one also involved a full respray, cold setting of rear triangle, (not generally advised on alu frames, but went slowly and it worked a treat), new decals, (again not date/model accurate), new wheels and tyres, new Campag Veloce 10 speed groupset and BB, new chain, new downtube adapters, new seat post, (24mm again), new Brooks saddle and bar end lights, new long reach brake calipers and cables, new headset and Aheadset conversion for new bars, new pedals, full mudguards, various new bolts and fixings and rear rack with light bracket
FWIW both these started out as sympathetic resto jobs, but both ended up being full on resto mods as you can see
Be warned though, if you go down this road you must either keep the bike forever, or accept you will never recoup the costs involved and just enjoy it for the journey. It would help a little if you used a desirable steel frame, both of mine were just HLE alu frames, but they rode really nicely when they were done, and I really enjoyed doing them.