What is a Marksman/ADC?
Marksmen excel at dealing reliable sustained damage at range, usually through basic attacks while constantly skirting the edge of danger. Although Marksmen have the ability to stay relatively safe by kiting their foes, they are very fragile and are extremely reliant on powerful item purchases & peeling from your teammates to become reliable damage threats. ADC stands for "Attack Damage Carry" which usually refer to a ranged hero who deals continuous damage with their basic attacks and scales with attack-related stats - i.e. attack damage , attack speed and critical strikes.
Usually, a marksman goes into the Abyssal Dragon/Bot lane with a support (Duo Lane). The support can be roaming or staying in the bot lane to pressure the enemies and protect the marksman from any threats/gank while farming peacefully. Marksman is one of the hardest role to play because they are so squishy, any mistake can be a fatal one and costs you the entire game.
A marksman have a few vital advantages over the other roles and playstyles. For beginners, marksmen are ranged which allows you to deal damage while being untouchable. However, marksman are too vulnerable to bruisers, fighters and assassins.
How to Play Marksman
1. Taking last hit on minions
It's important to learn to take last hit on every minions in the lane. On a regular minion (melee/ranged minion) you can get a bonus of 10 gold +/- and last hit on the siege minion (balista) would give you a bonus of 30 gold +/-. Let's say your enemies doesn't last hit and you do, in a few minutes you would have a few hundred gold lead and you can finish your first core item than your opponent which makes you stronger in teamfights or an Abyssal Dragon contest. If you are taking last hit under your own tower range, learn and get used to the tower damage, setting up last hit and take them comfortably.
2. Playing safe and farm
It's common that the enemy jungler would focus more in ganking marksman because they are the easiest target to take down. Try not to overextend if your teammates (support and jungler) are not around you, dying even once would be problematic (Bonus gold to the enemies, missing minions in your lane and potentially losing your tower). Most marksmen are weaker than any other roles in the early game, be patient, farm and get your core items. It's fine to use your abilities and sometimes your ultimate to clear the minion wave faster, it gives you more time to farm the jungle monsters or giving vision/protecting jungle for your team.
3. Knowing your objectives
It's better to take down the bottom lane tower than running all the way to mid lane to aid your team. By the time you reach mid lane, the teamfight would be over or you wouldn't be any help to your team. If your teammates are smart, they would try not to engage a 4v5 without you. Instead, they could try wasting their time in the mid lane to let you focus and take down the bottom tower. If you have successfully taken down the first tower, don't push further, you could risk it all. It's time to rotate to take objectives and taking tower other towers.
4. Positioning is key
Positioning is probably the hardest thing to learn on a marksman but it's the most important one. Keep your eye on the surroundings of your hero, try to focus, understand and react. As a marksman, you should NEVER stay in the front lines. You should always stay in the back, providing strong damage per second (DPS) for your front lines. By understanding the game and every heroes in the game (knowing their range, damage, abilities and cooldown), you can react based on each heroes' capabilities and knowing how much threat they could be to you.
Don't think what you are going to do next whenever in a teamfight. Think what your enemies are going to do next. For example, there is an assassin in the enemy team waiting for an opportunity to flank you. If you are the assassin, you would want to take down the strongest threat in the enemy team which is the marksman, if they aren't paying attention, you can take him down and win the teamfight. Know what type of enemy heroes you are dealing with, understand their gameplay and react to prevent these scenarios from happening.
Your main priority in the teamfight is to stay alive and dealing as much damage as possible. You should never walk into the front to focus on the enemy carries, leave that job to your team assassins or fighters. Stop mashing that attack button whenever you see an enemy hero.
1. The Blame Game
If you are playing a marksman poorly, don't blame the hero. Being a good marksman requires a good mentality thinking, blaming on your teammates or the hero are being in denial and you won't improve if you don't accept and learn from your mistakes. Sometimes it may be your teammates' fault for not peeling, but you can also play differently.
2. Bottom Lane over Top Lane
Sometimes, it's just better to head into the Bot Lane (even if the Dark Slayer is at the bottom side) as a marksman. Why? Because it's safer.
You have access into the bottom side jungle while farming it and being safe over the wall.
You can take the vision monster over the wall meanwhile you have to go outside if you are at the top lane.
Downside: You can't help your team when it comes to Abyssal Dragon.
But if the Abyssal Dragon is located at the bottom lane, it would be even better. 50/50 flip a coin.
3. Respect the enemies
If the enemies has a lead, respect them. A lead can mean many things such as being ahead in gold, items, objectives and experiences. It's more likely that you would lose in a 1v1 or 2v2. Sometimes you could even get ganked and dived under the tower. When it comes to this, it's better to give up and give the tower to the enemies rather than staying in the tower in a 1v3 situation. Things would get worse if you don't.
4. Correct item building
Learn what's best item for every marksman available and buy them accordingly, it's okay to purchase some defensive items if you are having problem with surviving. There is no point buying full damage items if you get assassinated before dealing any damage at all.
5. Being a carry
A "carry" does not mean that you have a lot of kills or dealing the highest damage for your team. It's more like making the right decision, giving calls and knowing what to do in a certain situation. You need a playmaker/shotcaller in your team so everyone doesn't go running around without any clue. If you can't be the one to do so, find someone who can.
6. No marksman meta/team composition
Don't worry too much about it. It can be hard to fight against a full-dive team composition where everyone just jump into you and burst you down but there are plenty of ways to win a game as a marksman. Start by playing more safe and scale into the mid or late game. The most common mistakes that people make is overextending and getting caught out of nowhere. Pay attention to the map and look which path you are heading. Your team support is your best friend and assassins/bushes are your enemies. Build your items differently rather than full damage, get defensive items to sustain - Frost Cape, Ancestral Glory and Death Sickle are great defensive items on a marksman.
7. Marksmen are a source of continuous damage
Stay alive, dealing damage on any target you can find. Even if an enemy carry are out of position in a teamfight, don't chase it and risk the enemy assassins to burst you down. You might feel that you deal no damage to the enemy front line tanks but actually you are helping way lot more than you think. Attack the enemies at maximum range and walk around after each basic attack, it helps dodging certain abilities from the enemies.
8. Rely on your teammates, don't go solo
Trust me, you will need your teammates more than ever. Have some faith and believe. You can't handle the entire game alone. Let them know if you need peeling against the enemies, flaming or being toxic wouldn't help at all.
9. Understand your enemies
What hero are they playing? What are they capable of? How to prevent it from happening? Playing marksman is not just understanding your own hero, but the enemies'. If you know what they are up to, you can prevent it before it happen. Otherwise you would just "blindlessly" play the game, basic attacking whoever you can without thinking what could happen next.