Read the owner's manual very closely and thoroughly. Clean the rifle and mags thoroughly to remove factory-applied preservative. Lube the rifle properly. Brownells offers a good series of vids on the Mini; strongly suggest you watch them after reading the Manual, and before workiing on the Mini. Buy several types of suitable ammo, and go shoot the thing, taking careful notes on which ammo types seem to work best/be most accurate, and stock up on them.
Strongly suggest you not modify the Mini until and unless you are 100% satisfied it is fully reliable. In the unlikely event you need to send it back to Ruger, be advised that Ruger takes a dim view of user-made modifications.
Manage your expectations; Your Mini will probably shoot a group about 2"-3" group at 100 yds, if mechanically sound and using good quality ammo. This level of accuracy can likely be improved somewhat with some minor DIY tweaks/mods, but test the rifle for reliability first.
Best wishes, and report back!