For an EM, there's pretty much only two classes of issues. 95% will be the same simple easy thing, the other 5% will be crazy weird cases that you hope you don't run into. Most of my EMs have been running for years without issues, and those 5% ones don't usually crop up during normal use

Start here:

http://www.pinrepair.com/em/index.htm

You'll want to print it all out so have plenty of paper & ink in your printer.

^^^^ this

If it really works as intended and you only play a dozen or two games a week, you should only need to worry about routine maintenance like waxing and replacing light bulbs. More than likely though, it's not exactly 100% and you'll need to clean some various things and adjust the gaps on some switches. It's all straight forward and Clay's guide will teach you just about everything you need to know. I'd recommend buying a box of replacement incandescent lightbulbs, some microfiber cloth, caranabu wax, some Q-tips, some 91% (or higher) rubbing alcohol, and a switch adjuster tool. That's a pretty good beginner toolbox for an EM. Also consider buying some new rubbers and a new ball if they haven't been replaced recently.

The more you play an EM the better off you'll be as far as dirty switches. Let an EM sit for 6 months without playing and you're guaranteed it won't work right when you do.