Depends on what you mean by running smoother. Probably the most popular mod is to install a Volquartsen hammer, sear and trigger. Won't make the action run smoother, per se, but it will make your MKII easier to shoot. You can also go into the action and do a bit of polishing if you're up to doing some gunsmithing.
Here's a post to this and other mods you can do. Mkiii: How to do all volquartsen upgrades, remove lci and magazine safety. You can ignore the parts about the LCI and magazine safety - you've been spared those on a MKII. Does have some nice hints on other things that you can do to your MKII, such as polishing the disconnector and so on. Plenty of sharp edges you can polish, once you get inside, but the disconnector is the one that has the most contact surface with the frame.
if you're not up to gunsmithing, just using standard velocity/target ammo, rather than the high velocity stuff will keep the muzzle from jumping as much and make the gun feel as if it is shooting smoother. Other than that, keeping the gun clean and lightly oiling the bolt assembly, as per the manual, helps things run smoother, BUT, the key is to lightly lubricate. Too much has the opposite effect.
The MKII is one of the niftiest guns made, and my personal favorite. It has everything that makes a Ruger pistol great, and nothing it doesn't need to make it drag. I've got a Government Model MKII with a heavy barrel. As-is, with no modifications other than "activating" the factory target trigger. Lots of folks are unaware that target model MKIIs have such an installed provision in their gun, which is a very nice, creep-free adjustable trigger. It just requires that you adjust it, as it was usually left alone by factory personnel, feeling like a standard trigger. The Government Model was made with very tight specs, originally for US purchase, and then to the public, and is for the most part the forerunner of the Hunter MKIII, sans barrel flutes. My favorite addition was the combination Hunter-style V-notch rear and lite-pipe front sight. This pistol was made to deliver mil-spec accuracy or better, and mine is the latter, a lot better.
If you've a standard MKII that lacks that trigger provision, follow North country gal's recommendations. I've done a lot of experimentation with ammo of many types and sorts. My personal favorite that I use in .22 bowling pin competition has been Federal bulk pack. It kicks the sawed off tops clear of the table by 8 feet, and shoots into 1/2 inch at 25 yards. For greatest accuracy, CCI Green Dot, Federal Champion, or CCI Mini-Mags are even better.
I'm up to six Standard/Marks, now, but, oh yeah, I've been on the prowl for the Government model for some time. Don't think a collection of Marks is complete without one. Thanks for reminding me to get back to work.
My wife grabbed mine off G..B......com in the last minutes of an auction while I was away one night and got it for $272.00. Bluing's in tough shape on the backstrap, but it's a keeper and an incredibly fun gun to pack in a holster when I take my Brittany for a walk through the woods with a pocket full of mags. Maybe I'll send it to Ruger for a reblue some day when I can stand to part with it for a while, who knows.
You've got some collection. Very nice. You know, I've seen the Government MKII in stainless actually more often than blue. I wish I could have grabbed one that was NIB, black grips, and went for $355.00 last year!!! Yikes.