About once a month, I get to play D&D in person. The rest of the time, I play with a group online. Using Skype for voice, Google Hangouts for dice, Roll20 for a tabletop and the aid of multiple screens, we manage to pull off a decent experience.
For in person gaming, I stand accused of decorating. The lights need to be just right, got to have the comfiest chairs all dragged together around the table and the books impressively piled. I even strategically place art supplies around the fidgety players’ seats. This is reinforced with table rules to limit distractions and cellphone use.
When playing online, you can't really control those elements. You can’t engage a player eye to eye or cart one off to a corner and hatch a scheme. If a player loses interest, they have the entire internet to turn to.
Here are some ideas to maintain immersion with a digital tabletop.
Be a beacon of focus. At first, you're going to have a hard time not talking over each other. Proximity in a real room allows us to focus on multiple conversations and let the group work through a decision. Online, they will need to talk one by one. Skype can quickly turn a conversation into a contest for the title of loudest. Slow things down and make sure quiet players have a chance to speak. You're going to have to be assertive about who you’re talking to and what information you need from them.
Music can be a powerful tool or a repeat distraction. Go for moodscape and sound machines over epic scores. For a lot of people, just having music will take up that extra part of their brain that would otherwise wander off to other parts of the internet. Keep it wordless and unidentifiable. You don't need people pointing out Lord of the Rings or Harry Potter every few minutes.
Dynamic lighting is one of the cooler features of the digital tabletop at Roll20. It allows DMs (with a subscription) to give players a line of sight. Light sources are blocked by walls and looking through a doorway only reveals what the light touches. It is extremely useful but invariably ruined by players inexperienced with the digital table that eagerly move their miniature, dropping themselves through walls or disappearing entirely inside a pillar. If you’re going to take advantage of this feature, you need to talk to your players about restraining themselves on the board.
Use a digital dice system like those in Roll20 or Google Hangouts. This is not about cheating—it’s about having a visual log of the die rolled. You cannot talk over each other, so if a conversation has moved onward while another player figures out a roll or decides on an ability, you can bring the conversation back around when you're ready. Check the log and give the result at an appropriate time. Plus, you can avoid the cacophony of dice clatters echoing through subpar microphones.
You might also implement a few house rules to keep the flow going.
In combat, group all alike enemies together. This is particularly helpful in miniature heavy editions like 4th. You get to move all your artillery in one go, all your soldiers in another. Speed along your turn to set a good example for others.
If a player doesn't know what to do when you reach their turn, move them down in the initiative for that turn. This is just about focus and keeping things tight, not punishing thorough players. Combat can be a very fun tactics game digitally, but it can drag on forever.
Use averages for damage. 5th edition actually includes these on monsters and abilities. Gathering dice is reduced to filling in checkboxes. There are no crazy dice towers or favorite d20s to search for. No point elongating the process of dealing damage.
As a general rule of thumb for playing with digital miniatures, if players are clearly winning, let them. Digital boards tend to put players in the mindset of combat advantage optimization over normal pen and paper play. You're the only one that knows The Rat King was supposed to be a mini boss. To players, he might just be some wererat who talks big. If the players have flanked you and cursed you with every manner of debuff, it’s okay to surrender or die magnificently to the next hit delivered. Design a better boss or battle location next time.