What do you use the bike for? If it was for commuting and canal towpaths, I would make different recommendations than if it was used for riding rough trails.
Check the tyres for age related cracks if they've not been used for a while, if check all cables and lube/replace where applicable..... Then bearings, check all bearings by dismantling and lube/replace as needed.... Then go out and have fun!!!!
Check the gear shifting, any problems are usually due to the ferrules on the outer cables settling in and making it look as though the inner wire has gone slack. Just need to tighten that up with the knurled adjuster at lever end of the cable (sometimes is at the other end).
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Then bearings, check all bearings by dismantling and lube/replace as needed....
Then go out and have fun!!!!