For all of the crying about Remington acquiring Marlin, I suspect your rifle will be reasonably accurate without any extra work at all.
Handloading is one route, but I have yet to actually top the accuracy of $15/bx Winchester PP's in mine, though I keep trying.
Trigger work definately helps, and spring kits for trigger tension are low cost, and easily installed. If you decide to "clean up" the surfaces, make sure you understand where things happen, or you can have an unsafe 336.
I'd be interested to hear about the bore quality myself. Many Marlins have a rough or tight spot, or two. I'm not comfortable with "fire lapping", but a few sessions with an abraisive cleaner, I use Remington 40X because it's very mild, will take care of any spots I have encountered so far.
Leverolution stuff may or may not shoot well in your rifle looking through some responses, like anything else. Not a big problem. The .30-30 won't turn into a 300yd deer rifle no matter what you feed it, and the stuff people have been feeding theirs for the last century has proven more than adequate. And still is.