Keep it moving
Since Mr. Autofire has, well, autofire, it's a good idea to just keep moving. Moving and evasion are highly important here since you don't need to worry about firing the weapon yourself. Take advantage of the several platforms that are around the map.
Keep dodging out of the way and keep moving. The enemies will try and follow you around. And since the gun is automatic, you just need to be nearest to the monster you want to take out. Quickly take out one target and switch over to the next one you want to handle.
Never stop moving though as that can spell trouble for you. Just because you're Mr. Autofire, doesn't mean you're Mr. Autosafe. Monsters in the game can deal a nice chunk of damage so keep that in mind. You have pretty good health, but it can drop quicker than you think.
Choose the best power-ups
When playing Mr. Autofire, you'll start to gain weapon upgrades as you advance. You see this in other run 'n gun type of experiences and the same applies here. Once you get through a level or two, you will be offered there upgrades but you only get to pick one.
It could be something like double the bullets per shot, or regaining health after a kill. There are several ones to pop up at random after completing waves. Try and choose wisely, and think about which one will benefit you the best.
The good thing is that, if you survive, you will likely come across one of the same upgrades that you may have considered earlier. So you'll have your current upgrade, plus the one that you decided not to choose but still probably wanted. Winner winner, chicken dinner.
Use double jumps
There's a lovely little double jump button that will allow you to make mincemeat of your foes. This makes things easier when you're trying to evade attacks. Plus, you don't have to worry about missing platforms as much which at times can put you in an icky spot.
Not to mention, using this feature allows you to kill with style. Jump over enemies and watch Mr. Autofire bring down a hailstorm from above. It's a good, safe way to kill enemies, just be careful not to land on the top of them as this will drain some health.
But utilizing the double jump feature is a great way to be advantageous with Mr. Autofire's "special power". The game is as much about evasion as it is attacking as we mentioned earlier. So go ahead and put a little swagger into your agile moves and kill like a legend.