If you only ski a few days a year, there's no reason to go nuts with working on your skis, but there's also no reason to ignore them either. A reasonably maintained ski allows you to carve properly and glide through a range of snow conditions and levels of skill.
You sharpen the knife for cutting bread, so go and get a full tune of your skis at the beginning of every season. Make sure this will include grinding the bases, bevelling and sharpening the edges and then wax. This should cost maybe $30-$50 and it's well worth it. Try to go to a reputable ski shop, not the discount store around the corner.
The hills usually have a shop at the bottom, but you'd rather be skiing, so probably not a good option... unless you can leave the skis there and pick them up next weekend or in the morning!
After the initial tune, you should maintain the skis throughout the season:
Every 3 days or so (especially before skiing ice), just sharpen the edges - it takes no longer than 5-10 minutes per ski. It is an important aid for carving in hard snow.
You can use either rough diamond stones or a fine file. The file takes more metal away but gives you a very sharp edge. As a recreational skier, you could just use the fine file - your edges should last through a few good years and then it's time for new skis anyways...
The diamond stones remove less metal (so you can use them more frequently) but they don't make the edge as sharp as the files.
If you get diamond stones, make sure you get the moonflex diamond stones they are more expensive but last a lot longer and do a better job. Get a coarse stone 100 for the hardened metal that appears when you bang your edges together or hit a rock and a medium stone 200 for polishing after the coarse stone or the file.
The problem with stones is that they are more complicated to use, require cleaning and cutting the sidewall etc. A file is generally rough enough to remove that plastic just above the edge as well, without gumming itself up with it. If that's an issue, get a "sidewall rip" at a shop.
You also need a 2 or 3 degree edge guide, as seen in the video (select your bevel angle fromthis chart). Just for reference, for performance skiing, I use 0.5-1 degree on the base and 3 degrees side bevel on all my skis - it keeps things simple. You don't need to worry about the base bevel.
Expect to pay $20-$30 for the edge angle guide, chrome file and diamond stones, each. As long as you have a guide and actively maintain the sharpness of the ski's edges, you're ok.
What I do for everyday skiing is to use the 200 stone with a few passes and leave it at that. Every now and then I start with a fine file and finish with the stones.
Get some some rub on wax - I prefer something solid, not paste. Ideally every day, but as often as you can: rub it into the bases and work it in with a felt pad. It takes maybe 5 minutes for 2 skis and you're done!
Keep working it in with the felt pad, until it looks nicely even and polished. Don't worry about scraping or brushing it - you'll ski it off anyhow :).
This should last maybe half a day... which is why you would start thinking about hot waxing your skis eventually: because it would last the entire day.
One other method you should probably take into account is Hot waxing the skis with a heat gun.
Up to you! Good luck!
Read on for even more Ski Tuning Ideas.
Or, see the Swix www.swixsport.com Easy Preparation guide, under Download/tech manuals (their webiste links are too bad to paste here).