I can give you a bit of my perspective on this one. I'm currently playing in a game that I used to attend face-to-face prior to moving about 6 hours away. These days, I'm participating in the game via Skype and d20Pro (previously, we used MapTools).
From my side of things, the single biggest help has been the addition of the webcam showing the other players. When it was voice only, I frequently had issues of wandering attention and such due to getting left out of conversations. There were also times when too many people speaking at once on their end came across as a garbled mess.
Since they added the webcam on their side, I've felt much more involved because I can see them once more. I can see when the gnome sorcerer is nodding off after a long day of work. I can see when the human ranger is pulling out the extra bag of dice before combat to get ready for rapid shot.
Since we use d20Pro to present the maps to the players and Skype runs on a different system that only the DM sees, they don't view my webcam. It just means they don't see me sitting at the table. Sometimes, I wonder if it might work a bit better if they had a dedicated netbook or system running just skype with a monitor positioned where I normally would have sat to help create that illusion of my being there, but it's a topic I haven't broached with the others.
In general, though, I would say that if you are the DM, most everyone will already be focused on you. If you are connecting as a player, do what you can to contribute to conversations and discusions as that will be the best way to remain involved and invested in continuing in the game.
Beyond that, I second what Treebore says. Jump into a game. That will be the best way for you to learn how gaming online works.
Happy gaming.