I wonder, when I put my guitar somewhere, without anybody else drop my tuning, the tuning sometimes drop down a bit.
How to make the tuning just stick on the right tune? Is there any tips or tricks?
It's pretty well the nature of the beast.That's why the tuners are accessible. Expect it to happen, it will.Professionals tune up between numbers - or get their roady to give them a freshly tuned different guitar, so why would we expect anything better? Classical players are blighted with the same.So whether it's being used, abused or left to rest, it will sometimes go out of tune.
This problem will never completely go away, but here are some ideas to try:
The humidity and temperature that you keep your guitar in, will have a massive influence on it's tuning. If it gets hotter, then everything stretches and there is a good chance that your guitar will re-tune itself higher. If it gets colder, then the reverse happens and that lets everything contract, potentially allowing your guitar to tune itself down. It is just the nature of physics.
Contrary to other comments, you should always use new strings, as often as you can afford to get them. Certainly more often, if you play regularly. Definitely replace any strings that are blackened or appear corroded.
Pretty much impossible, the strings inevitably will be losing their tune as a function of time. Just tune up more often.