Good communication is the key to victory, and it still applies when you’re playing with a friend. Here are some things to keep in mind.
Have one of you time summoner cooldowns. You have to be extremely optimistic to rely on your teammates when it comes to this, and it gets worse the lower the Elo you play in. Ideally, the duty is assigned to the person who has more time to look around.
The default algorithm would be Support>Jungle>Top. However, if one player is much more experienced than the other, perhaps they can take the mantle even while playing a micro-intensive role such as Mid.
Keep using pings. Even if you two understand each other without them thanks to VOIP, remember your other teammates can’t hear you. Let them know when you’re moving around or setting up a gank. Yes, even when it’s a gank that supposedly has something to do only with you. Top and Jungle players will appreciate the info so they can come around if they have the time.
Also, use pings wisely. It’s great fun to spam light-hearted question marks when your teammate makes a stupid mistake, but it distracts your three other guys from their gameplay. Also, it’s straight up annoying. Sorry.
Don’t do this
Play roles that synergize well. The bottom duo is, generally, a great choice; you should be able to beat random enemies with similar or even better individual skill. Once you’re doing well enough, it’s possible for the Support or even both of you to move around and boost your teammates.
Mid+Jungle is awesome, too. In most metas, a snowballing champion with great stats can pretty much carry the game. The middle lane being in the middle enables you to interact a lot and extend your lead to objectives and monsters.
Jungle+Support works when your random ADC is mature enough to avoid dying while alone. It means you can gank Mid and the enemy Jungler together. If the ADC is immature or inexperienced, coordinated assaults on the bottom lane are nice as well.
Avoid reflecting too much in the game. I have a few pals who try to think too much about how bad their play was or how busted an enemy champion is. Sometimes, they even start blaming the teammates they’re sitting in the VOIP chat with. Screams may help blow off steam, but generally, they don’t bring you closer to victory. After all, the morale of your partner could take a hit.
Also, avoid diving into your random teammates’ mistakes. Arguments are pointless, as they won’t become better within 10 minutes, and you end up wasting too much time typing. Find your team with DreamTeam and focus on your play instead.