How often should you tune? The answer really is...constantly.
That doesn't mean that you should take them to a shop for a full edge grind every day--you definitely should not
do that! But it means that you should get them tuned, and then maintain that tune.
A tune begins to deteriorate the moment the final stone leaves the edge. It's like a tune-up in a car, or new shocks or tires, or a haircut. You may not notice the change moment by moment, but you sure can tell the difference when you get that new tune-up. If you want to develop your skill and technique to their best, and if you seek consistency at your highest level, you need to keep your equipment up.
It's not that hard, actually. You'll need a few basic tools (see slidewright.com
and be sure to ask for your EpicSki supporter discount), a little practice, and just a few minutes a day. A pocket diamond stone or two (medium and fine grit) and some fast wipe-on or spray-on wax will do wonders to keep your skis working well.
Get your skis tuned by a good shop. Let me repeat that: a good
shop. Then use your basic tools regularly to maintain the tune. Have the shop tech or a good
instructor show you how to use the stones, if you're not sure. Inspect your skis every morning before you ski. Run your finger gently along the edges and feel for burrs and rough spots (be careful not to cut yourself). Use your stones to smooth these spots out, and then run your stone completely along the base and side edges to touch up the tune and keep them sharp. Wipe on some wax, and you're good to go for the day--shouldn't take more than five minutes. Check your edges periodically throughout the day--especially if you hit a rock or something. A few seconds with the stone are well worth it!
In normal condtions, that's all you'll need to do. Get 'em tuned, maintain the tune, and enjoy the consistency and performance you're capable of--much better than getting 'em tuned and letting them deteriorate until you can't stand it anymore, and then getting them tuned again to a level of performance you're not used to, and can't take advantage of.
The only reason you should need a major re-tune is if you do serious damage to your skis, or perhaps if you encounter vastly different snow conditions. If you're only skiing deep powder, you probably won't hit many obstacles, and you won't need your edges to be very sharp (but you'll still want them smooth and burr-free). If you're skiing rock-hard ice all the time, you'll want to keep them razor-sharp, consistently, and those conditions will dull the edges even if you don't hit obstacles, so you'll want to spend a bit more time each day. With a little practice, you may become intrigued enough to want to invest in more tools--files, bevel gauges, a waxing iron and tuning bench, and such, and develop the skills to use these. You'll find lots of good advice on the Slidewright website I linked to above, and don't hesitate to ask more questions here at EpicSki.
But again, the key to your best performance is consistency. And the key to that is continuous basic maintenance. Don't worry--it's easy!