Hey man,
You should touch the girl *within the first few minutes* of ever interacting with her. It's a brief touch, "incidental", to start with. Get used to doing it systematically. If you break the touch barrier very early on, it will make it way easier later when you move to more romantic or sexual touching. If you wait before ever touching her, it will be awkward. The more you wait before first touching her, the more awkward it will be.
Here's how you can pull incidental touching. You are chatting about casual things. You reach a high point of your conversation, and just at the same time, you briefly touch her forearm. It will appear as you are just highlighting what you are saying (your high point). Continue the conversation normally (there is no gap). After a little while, you just repeat once. It's a very brief and subtle touch. Again, you need to pull it off at the very early stage of your interaction with her.
You may notice that, after that, she will touch you back.
Later, you can be more daring in your touch. It's no longer incidental, but deliberate. I posted
this for a more general guide on touching and escalation. The main GC site has many posts on touching and escalation.
About sitting across each other. You should avoid it if possible. It is more confrontational position (body language wise), and it makes it harder for touch and getting physical. I always sit my girl beside me. Closer to me makes it easier to hear her, to touch her, to get physical. And it is much less confrontational position.
Good luck
Seppuku
