First, you have to pick an easy song that you know well. That song should have keysounds.
Then:
- Autosync the display lag
- Autosync the audio latency
Mute the sound, check the box "autosync" next to the "display lag" box, set the speed at your comfortable level, then start playing that song.
Try to press the key at the same time that you see the note hits the judgment bar. Ignore the judgment that it gives (open2jam will adapt to your timing).
Turn the sound back on, check the box "autosync" next to the "audio latency" box, make the speed a little bit slower, then start playing that song.
This time, try to press the key at the same time that you hear the sound of the music. Ignore that the notes may already passed through the judgment line when you pressed the key (open2jam will adapt to your timing).
In other words, try to make the sound of your finger hitting the keyboard in sync with the sound of the music.