Tuning an ukulele for the first time, you might wonder, “What is wrong with this instrument? It just won’t stay in tune.” Some conclude that, “The tuners must be slipping,” but if you have geared tuners, this is usually not the case. It is natural for new strings stretch out for the first few weeks of use until they ‘settle in’ and stay in tune for more than a few minutes.
However, if you’d like to break your new strings in a little faster, I suggest that the first time you tune them that you tune them to Canadian tuning: ADF#B (reference notes on ukehunt), a whole step higher than standard GCEA. What then? Walk away from your ukulele for a few hours (or a day) . . .
When you come back to your uke, it will be much easier to tune to GCEA and stay there for a longer period of time. Tuning the first time to Canadian tuning will not likely hurt your uke either, as thousands of Canadians tune it that way every day.
When you tune GCEA, the easiest way is with an electronic tuner, but here is a video reference to tune to if you need it: