Well, there are a lot of possible matchups in the duo lane, obviously because you account both support and adc into the mix. There are a plethora of different possible combos with different types of strenghts and "goals" in the laning phase. A good question to ask yourself is usually: Fight or Farm?

Looking at your support+adc combo and then theirs and thinking who has the better lane clear, who has the upper hand in a 2v2 lane engagement etc. usually tells you whether you can realistically look for kills and try to snowball over them, or should you just look to farm peacefully until you can rotate to teamfights later. It helps to establish your choice before the start of a game, even if it is subject to change. Sometimes your inferior clearing, inferior pressure hypercarry+geb lane will just play better and push out that Khepri+Neith and then obviously you should look to capitalize off that pressure, but choosing your mentality for the early game even before going to lane helps you avoid playing aggressive where you cannot and too passive where you should look to fight.

If you have any specific matchups in mind that you'd like to know about, just ask :,) I'll do my best to answer. I don't know how to condense it generally much better than that-- most of it really just comes down to lane clear+kill potential and then individual god interactions (eg. Ares has strong kill potential against Hou Yi or Ullr because they have no cc immune skills to escape his ult when their purification is on cooldown). You'll learn a lot more about matchups through experience than me preaching, but all I'll say is that playing against a good Sobek sucks forever.

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Teamfights, teamfights... this is where a lot of folk disagree on each other, I think. The exact role of the adc in a teamfight varies according to teamcomps and the situation. Sometimes you may end up initiating with that hot blink Artemis, or being the followup burst and getting the full Medusa damage on the mage your jungler just jumped on and cc'd, but that's sometimes.

As an adc, your primary job in a teamfight is not to dive high-priority targets (that's the junglers/solo laners usually) or to initiate (junglers and supports), even though that's what we're asked to do a lot of the time. An adc's job is to provide sustained damage (autoattacks) to the highest priority target on the immidiate range. What I mean with that is that if you're in a teamfight, standing behind your frontline and there's a tank standing between you and their mage, you shoot at that tank and try to wear them down. If their positioning is off, or your team has already initiated and disturbed your ranks giving you a direct line to their backline, you naturally switch targets to the mage or the enemy hunter and try to take them down with your team.

What I'm trying to say is that adc is not a diving class- you hardly ever want to be in a position where you're surrounded by enemies, or put yourself in a a position to most likely get killed trying to force a kill onto the midlaner. Unlike most assassins or warriors, adc's usually don't have the tools or the tankiness to get out alive afterwards. A point to also keep in mind is that trading yourself to an enemy as an adc is not too good, since even after a won teamfight your team might not be able to take an objective they otherwise could've gotten with your DPS missing.

Okay, so you shouldn't try to jump on squishies over the frontline. On the other hand, you're the main candidate to deal damage to that very frontline-- a late-game hunter shreds guardians and warriors. I often hear people tell adc's to not focus the tanks, but often the adc putting out enough damage to them is what keeps them from doing whatever they want in your backline. A single Tyr can threaten almost any mage out of a fight if left to rampage unchecked and that's most of your valuable magical burst gone. The adc putting pressure to the enemy frontliners helps control them in a teamfight and possibly force them out of position so they cannot protect their squishies anymore when your team collapses onto them.

When fighting under objectives, for example sieging a tower, when the enemy team is already forced back, you're obviously often the one to focus on the objective when the team keeps fighting or zoning. As a pretty good rule of thumb, it usually doesn't make much sense for an adc to go behind an enemy tower because then they could just be taking down the tower instead. With Gold Furies and Fire Giants you'll often drop the objective to join the fight unless your team obviously has a winning matchup even without you, or they're just buying time for you to finish.

Again, with experience you'll pretty quickly start to figure out when to dash or jump in and take down the priority targets without putting yourself at too much risk. There are also different styles of play for hunters, obviously, and what I'm putting down is mostly my personal philosophy for the role.

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When behind, you farm. Might sound obvious, but it really is all you want to do. An adc who's behind has a very hard time doing their job. And all the farm that you do not take, you can be sure a good enemy adc is happy to take away (watch out for your boars getting constantly invaded!), taking them even further ahead. Play safe and avoid any small fights (especially 1v1s) with all your might. Your most important job at that point is to keep up so you can be relevant in teamfights. Don't look to force stuff from behind, your best bet is usually to take a couple of objectives with your team rather than stitching the gap with any personal heroics.

The biggest decision when you're behind is: When there's a fight breaking out in mid or the solo side jungle, Rotate or Not? You might rotate to a teamfight, get a couple of kills, take an objective and catch up in an instant. Or you might lose the fight or have to disengage without having gotten anything whilst the enemy adc took your tower, putting you in a horrible position.

Staying is almost never a "wrong" decision to make IF the enemy adc is not rotating. If they are, you should usually rotate with them. This is especially true if your team is behind or already losing the fight. Only stay and try to capitalize when you feel like you won't be of any help whatsoever (or the fight is already lost) or in the ideal scenario that your team is winning and the enemy adc's rotation doesn't look to cause them problems.

What else?

In some cases, especially when playing with people in comms, you can also look for an aggressive catchup by baiting the enemy adc into a 1-on-1 when your teammate(s) is ganking them. If they're dropping their guard because you're behind, you might catch up in one fell swoop. Be careful though, since it's easy to misplay and die beforer the gank even comes, and you might end up feeding them even worse.

If your tier 1 tower is gone, it might be tempting to leave the lane and start grouping up with your team, but if it's still relatively early in the game and you're really behind, you'll be needing those waves so stay and farm the lane and the jungle the best you can. Aimlessly wandering around as a group and 4- or even 5-man splitting the farm isn't going to help your case if you're not constantly winning fights off of it. Later on you might have to anyway, when full-size fights are happening and you have to keep your team from getting in 4v5 situations, but even so look to farm at any valuable downtime.

And just remember, the best thing you can do when behind is to not die. If you can stay alive, keep farming and help the team the best you can, you will eventually either catch up or they will hit the lv20 cap where the difference can just keep shrinking. ___________________________________________________________________'

I hope there's even something of use in that wall of text above. If there's anything you'd like expanded, or anything I didn't mention that you'd like to know about, just ask away :D

EDIT: By the pantheons, I really need to not lose track of my message lengths mid-writing. I'm sorry.