TowerFall might be a fast-paced arena game with dash-jumping and high speed arrows, but it's also a tactical affair. Yeah, alongside of all that arrow slinging you'll actually need to think from time to time, and there are a few secrets you can use to become the pride of your local group of friends.
First things first, master the dash, as it's core to your success as an archer. Start off in a "break the target" level in solo play to really get a feel for movement, as you're going to need a bit of practice. Each level will teach you something new about the game, both in terms of core concepts and power-up use, so think of them as a tutorial. While you're breaking targets, note that dashing while aiming towards the ground will result in a slide, allowing you to slip underneath low ceilings. You can also jump on targets to break them and save an arrow.
Like most action games that have a wall sliding mechanic, the dash has an invisible cooldown that prevents it from being used again -- learn the timing and you'll go a long, long way. This is mostly because the dash isn't just a method of movement, but also a way to grab arrows out of the air, which blocks an attack and grants you ammo. It's not a foolproof tactic though, because enemies can follow-up with another arrow after you're vulnerable. To counter this, don't dash directly at an opponent who has more than one arrow -- keeping an eye on their arrow count can sometimes mean the difference between victory and defeat. Movement tactics soar beyond that one move though, as there are a number of things you can do to fake out your rivals. Similar to the Super Smash Bros. series, you can grab any ledge in the game and just hang there. Grabbing on a ledge to trick your opponent into firing a precious arrow, then leap up (or dash straight-up) and counter-attack.
You are limited in terms of your finite maximum arrow count, so you need to master locating them like a sixth sense. Look for them wedged into walls, floors, enemy corpses, and even the ceiling. Pick up every arrow you come across (if you can hold it), as you never know when you might need it. Note that arrows have a "light" homing ability when you're aiming them near enemies -- so the closer you are, the better. While power-ups can certainly change the tide of battle, don't worry about them too much, and don't prioritize them over kills. I can't stress this enough -- be smart with your arrows -- this isn't a shooter by heart, so keep a steady flow of concentrated shots followed by arrow retrieval until you start to visualize potential paths in your head. Once you start to play more you'll naturally gravitate towards picking up spare arrows, and you'll never be without.
You can also use a more outside the box tactic when aiming by using the "stage loop" to your advantage. You know how in Pac-Man you can go into tunnels and come out the other screen? You can do that too when there's a loop (a gap in the map), and so can your arrows. In the heat of combat with four players, practice shooting errant arrows into the loop and watch the kills wrack up as everyone tries to figure out what's going on. Also, shooting your arrows through a fire source makes them fire arrows.
Co-op quest mode is the newest addition in TowerFall: Ascension, and given how many enemy types there are it will take a while to master. Remember that you don't have to kill everything here by way of an arrow; jumping on heads is often the most prudent course of action. Every enemy also reacts differently, so pay attention to their patterns. For instance, the grim reapers will dash back and then lunge forward with their blades, catching you off guard. Because of this, it's best to surprise them from above with a stomp on the head. Ghosts will dodge your arrows, so the same thing goes for them -- stompy stompy. You can use the vertical stage loop to your advantage here, always ensuring that you have the high ground to aim your stomps.
It's amazing how complex TowerFall is, despite the fact that it looks like a simplistic arena game on the surface. Just aim true and don't waste your arrows and you should achieve some level of success.