The last one was incomplete and lacked vital information. I might include info from the old one, possible deja vu for someone who actually read it
RBY's runner guide
Because the runner isn't just a flag carrier Basic info
The runner is a versatile class. He is incredibly useful both on offense, defense, or anything in between. His purpose on the battlefield is harassment, offensive support and achieving objects quickly. Your mobility allows you to flank the enemy team better than any other class could.
Despite this, the runner has some weaknesses: He has a short range, bullets spread greatly and he has low health. The runner requires you to get close or even inside the enemies sprite to do serious damage, and this gets difficult at times with the 100 hp. Anything with decent aim and firepower can take you out quickly if you mess up. This is why the runner isn't fast only as a class, he requires fast thinking and decision making, both on macro and micro level.
Micro
Micro would refer to dancing or engaging in battle with an opponent(s). Because the runners low health, it's vital that you take as little damage as possible. To do this, dodging and dancing will be required. Dodging is pretty simple. Like it suggests, you dodge projectiles and particles that are coming your way while you try to get close to your opponent or, on the contrary, while you are trying to get away from him.
Dancing, on the other hand, takes this to a whole new level. You get as close as possible to your opponent and you don't dodge based on where the bullets of your opponent are now, you dodge based on where they WILL be. This requires you to always be one step ahead of your opponent, or even multiple if its a push of more than a pocket and a medic. But how do you know what your opponent is going to do? Magic? No, prediction, one of the most important skills necessarily for a runner to survive and for him to be useful. This skill can't be taught by mere words. Only by playing this game a lot, you'll eventually know what your opponents are going to do because you have seen it multiple times and you'll be able to work towards that.
Because of how bullets come out from most classes, saying in your opponent's sprite is basically the best way to battle. The enemy will try to get you out of his sprite by moving towards one of the directions available. If this is just flat ground, your opponent is out of luck, the terrain is ideal. But if he has multiple escape routes, some even leading you down a small hallway (pits near the point on koth_contra, koth_valley, as a simple example), the heavy can use them to counter you. He can move himself towards that and try to make you follow him. He'll be able to spray you while you are going down to follow him. Now, you might think ''Oh, I could just dodge his attacks and get close again'' Perhaps, but not on this terrain. I've never seen a runner dodge a rocket when he can't get out of its way or jump

Now dancing requires a lot of practice. Your opponent may not move the way you wanted him to move and he'll mow you down if you don't quickly respond to his movement. Practice, try different ways of approach, or going for the medic instead of the patient. The more you do this, the better you will eventually become.
Push your limits and have fun while you're at it.
Actually a great piece of advice regarding this subject.
Having the higher ground or the advantage of the objective is also a major advantage when it comes to fighting. Having this ground would refer to being in a position where you are at advantage compared to your opponent. For example, you are defending the intelligence on ctf_2dfort
Dat horrendous quality
The red runner is obviously going for the intel you are defending. From where he currently is, he only has the option of going straight ahead towards you. If he chose the other route while he got out of the spawn, things would of course have gone differently.
But right now you have the upper hand since he doesn't have a choice. Capturing is the essence of ctf and that's what he's trying to achieve. The timer is running out so he can't wait for support, he'll have to try and take you out right now, and there is only one way: Coming right at ya'.
Backpedal. He has to run into them because of the cramped terrain. There is no possible way he can dodge it. Another way would be spamming momentum shots at his, but you'll be open to attacks yourself. Surviving while you are the only person defending is still one of the highest priorities, else the intel would be right open and the other team won't get any opposition. Again, use prediction to your advantage here if the terrain isn't so cramped.
Macro
Sure, you fight well and know how to take people out, but is there a point if it's not any good to your team? Macro would refer to how well you fare on the strategic level of the game. What choices do you have to make in order for your team to win? What will be the consequences of you picking out that single opponent for both your team and that of the other one? Do you retreat in order to go back to your team mates and help them out with a push, or are you going to attempt a back/solocap? This class will constantly force you to make these choices quickly. It's a team game after all, try to be beneficial to your team instead of being a burden. Playing often will make this choice making easier, because again, you might be able to quickly predict what will happen if you do either of the choices you thought of.
Macro might also mean how good you can (take) control (of) the part of the map you are on to make sure your team has the most terrain. Holding terrain is everything in CP. Lose it, you'll be pushed back and most likely killed/
Use your mobility to play tricks with the enemy that will help your team push further or get the upper hand in battle. A common example of this is abusing the lower route on ctf_conflict at the start of the match. Quickly roll out and immediately take the lower route. From above, someone or some people might notice you and notify their team of your presence, and in the best case, go back to defend because they assume you are going for the intel. Now quickly go back to your team and help them in the push. You'll notice that the enemy team will be above their spawn or near the intel because they were waiting for you, and your team will have pushes through the mid with little opposition. Even simple taunting after a kill will make some opponents lose his cool and forget about the objective and focus on revenge. Use this to your advantage.
Another way to put mind games is simply manipulating someone's decisions. For example:
Red The enemy team
Blu Your team
Yellow You
(see what I did there!)You're in the excellent position for being a distraction maneuver. Your team can't push ahead because of the enemies. Drop down on them and do as much damage as possible. Of course, you versus an entire team won't go well, but an alert team will get what you are trying to do: distracting them. Your team should take this chance and mow them down while you are shooting them in their confusion. In most of the cases, this will secure victory if your team survives.
Essentially: Behind that sprite you see is still a human, and humans can be manipulated (;
Flanking and double teaming
Because of the runner's amazing speed and double jumps, he is the class most suited for flanking. Of course, flanking would indicate that you attack from the side that the enemy team isn't facing as your team is fighting them from another direction. While they are forcusing on the team, rapidly take them out. Go for key targets such as the medic or the main member of the enemy push, usually the pocket.
Do note this:
How good you are at flanking is how good your team performs. If your team is bs you won't get good enough opportunities to flank the enemy. If they die too quickly, the enemy team will focus on you instead of your dead teammates. Your team also has to create chances for you (like distracting) so you can get a chance to flank someone. No good team, no good flanking possibilities.
Picking and hammering
Picking is going for a specific person (usually, the medic) while his team mates are trying to defend him. This person will often have full health but taking out key targets is what you should be doing. Hammering is finishing off already weakened enemies by your team. Decide quickly who you pick or finish off. What is the most helpful to your team? The pocket soldier that is the other team's main offence, holding your team back, or the medic, who's keeping him alive. You either go for the medic first and the soldier will try to take you out (most risky and most rewarding), or you go for the pocket soldier first while the medic heals him (less rewarding, easier). Whatever you decide is up to you. Think of the consequences for the remainder of the battle, and prepare yourself for those.
Video tutorials
I think this should cover it for now. Anything you want me to give an opinion about or include into the guide, feel free to ask