I design layout (buttons, labels etc.) on my galaxy s2, once I install the app on tablet
all the stuff is located on upper left of the screen
how can I do something that will adjust the locations of all - at least on middle & center of the screen?
or is there a better generic way to do this?
You can use anchors and/or the designer script to change behavior on different size screens. Another way is to create two layout variants. One for phones and one for tablets. Look at the Beginner's Guide, chapters 8.9 - 8.11