Simple things to do to minimise tuning problems:

1. When you put new strings on, don't let them overlap themselves on the machine head peg, or they'll slip forever.

2. Change strings as often as you can afford. And them clean with something like Fast Fret.

3. Buy a set of Gotoh's, 1:18 ratio. Best machine heads in the world. My Taylor came fitted with the worst machine heads in the world. Whatever they were, they soon got changed and I eventually did the same on my Martin. Both guitars are miles better now.

4. If using an electronic tuner, as I do, make sure the battery is good. If the needle (or lights) start wavering excessively then either the battery or the strings are on their way out. Don't forget the pick-up battery if you plug in the tuner.

5. Still on tuners, once the guitar's "in tune", you may need to make fine adjustments to get it ringing properly. The top E on my guitars always needs to be sharpened just a touch (so suspect the tuner!).

6. When tuning, always tune "up" to pitch, i.e. from flat to sharp, so that the tuning peg bites on its cog. If you tune from sharp to flat, the string will go flat as you play.

Pete