Weakening or killing:
If the enemy has less than 150 HP, a shot 1 will kill them and uses less delay than a shot 2. That lower delay might be helpful later in the game. It's also safer because 1 makes a bigger explosion when it misses than shot 2 does, so if the enemy is barely alive, a near miss can still splash them for a little bit of damage and kill them, while a near miss shot 2 wouldn't hurt them at all. Also remember that a full hit from shot 1 will do better damage than a half-hit from shot 2.Shot 1 also can be used to set up a kill. In theory, almost any enemy can be killed with 2 duals. But in reality you will see that some bots have high defense and your dual doesn't do the 'expected' 500+ damage. If your dual takes off less than half their life, then you probably need both a dual and an extra shot 1 to kill them. It doesn't matter whether whether the dual comes first or the shot 1 (in terms of damage), but it's good strategy to use shot 1 first. An enemy with more than half his life thinks "My turn's coming, should I dual or not? Since I have so much life left, I won't dual yet. I'll probably get another shot before I die." If you use a dual on an enemy who is thinking like this, he may change his mind and say "Now I'm almost dead. I'd better dual so I do lots of damage before I die." But if you use the shot 1 first, the enemy may not realize he's about to die because he still sees he has "about" half his life left. You're also guaranteeing that if you screw up, you at least don't use up a ton of delay and give the enemy 2 shots in a row against you.
Beating the enemy's delay:
At the opening of a match, if the enemy uses a fast shot 2, then you may not be able to beat their delay with your own shot 2... but a shot 1 will work. A lot of players understand delay in these simple terms at the beginning of the match, but later in the match there will be chances to win delay as well. If you haven't already, click the button that shows the "Turn list". It's the little curved arrow at the top left of your status bar.Watch the delay numbers for the enemies below you on this list. If any of those enemies show a delay of 800 or higher, then you can use a shot 1 and get another turn before that player can shoot again. (The same idea can be used with shot 2, but you need to look for delay higher than about 900). In most situations, if there's a chance to beat the enemy's delay, you should take it. The exception is when an enemy needs 1 more dual to kill, and you have a guaranteed shot on them. In those cases, just kill the enemy, don't waste a turn beating their delay if you know you can kill them right now.
Also, be aware that when most bots fire a dual at the start of the match (or any time their delay is about even with yours)... they are giving a huge delay advantage. The delay advantage is so big, you actually have time to fire two fast shot 1's, and then still get another turn before the enemy can shoot again. If all your shots hit nicely, you can do about 900 damage to them before they get another turn.
Dealing with no angle:
If you're on fairly flat land and cannot get a good shooting angle for shot 2, then just use shot 1. Eventually you'll probably get angle (either by walking to the nearest slope or by the enemy breaking some land near you).
Creating angle:
Sometimes the nearest slope is so far away, it would take 3 or 4 turns just to walk to it. And some enemies won't help you out by destroying the land and giving you an angle you can use (for example if a Turtle hits you directly, it won't even touch the land below your feet). In those situations, it is smarter to just create your own angle so you can start using shot 2. If you try to pound the enemy with shot 1 all day, and they're doing almost twice as much damage with their shot 2, then you are sure to lose. But if you create an angle that allows you to hit with shot 2, then you have a chance. Just fire shot 1 directly behind you (not in front of you, or else you have to walk all the way to the front of the crater you just made).If you're stuck deep in a pit, and the enemy has just ruined your angle, then the smartest thing you can do is get close to the wall in front of you, then turn and fire shot 1 a bit behind you. You waste a turn now, but you'll have the needed angle for your next turn. Also, by staying close to the wall you can hide a bit from your enemy's next shot. The stupidest thing you can do is to cling to the wall and try to blast through all the land in front of you. Turtle is not good at blasting through dirt and it would waste a lot of turns trying to shoot through so much of it.
Ruining their angle:
The situation shown above is something you can do to the enemy, if you have sharp aim and use shot 1 . Look for opportunities where an enemy is deep in a pit or very close to a steep section of land. Try to plant your shot 1 directly in front of their feet, without hitting them directly. Your goal is to make a nice round hole in the land, not to hurt them. By doing this you can 'steal' a turn from them by forcing them to waste a turn creating a new angle or blasting through land. Sometimes, if the wind is helpful, you can do this over and over, splashing them for a little damage each time while constantly ruining their angle. Remember how I mentioned earlier that it's possible to get 3 turns in a row against an enemy if they fire a dual as their first shot? This is a good time to practice your angle raping skills, especially if the enemy is already bellied up close to a steep slope. You can fire a pair shot 1's in front of their feet to create the kind of hole that ruins their angle, then try to hit a dual shot 2 directly onto their back. If everything goes correctly they will have taken over 600 damage and have no angle.