Mods really depends on the action and how it feels, if the gun is real tight it may need some stoning. You can hour glass the mainspring for sure. If it is very old a good cleaning, I mean good, get in all the nooks and crevices, will help it too. While you are cleaning check the left extractor, it should have a long tail, if it is short it is broke and needs replacing.
Keep it clean, lubed and after a shoot or two use a chamber brush on drill motor to clean the chamber to clean the plastic and lead. These guns were not made for the shells we shoot today, and if not cleaned in this area, eventually a shell will hang up and make the action almost impossible to open.