adb install example.apk
adb install -s example.apkandroid install apkadb root
adb push my-app.apk /sdcard/
adb shell
su
mount -o rw,remount /system
cd /sdcard
cp my-app.apk /system/app
# or when using Android 4.3 or higher
mv my-app.apk /system/priv-app