1) "sticked" pegs (the pegs are hard to move, and tuning an impossible mision): take a smooth sandpaper and pass it by the peg. Just a little, then insert the peg again and check how it rotates. Pass the sandpaper again if necessary. Be careful, it's easy to get a toothpick if you insist too much with the smoothing...
Another way (better if you have black-stained pegs), is to pass graphite (just a simple pencil) by the peg.
2) "slipping" pegs (the pegs can't stay in their sites, and strings become loose suddenly): put some talcum powder on the peg. Anyone is helpful. This will strenght the contact surface between peg and its hole.
Another way is to rub a candle against the peg, to get some wax on it.
Hope it helps!
* * * * *