You can get 600k at the end of the second level.
I used the slow fighter with the first shot option, the middle missile option, and the first behind option.
Note that your score constantly increases as long as you fire, so always be hammering
for extra points.
Proceed through the first level. Pick up power ups and stay alive, as the only real danger is slow moving orange bullets. Stay to the back of the screen and avoid them. Your missiles will shoot a 45° angle so use them strategically to destroy ground enemies while shooting ships in the air.
Once you get to the boss, simply stay at the left side of the screen while shooting at him and avoiding the orange bullets. Don't worry about maximizing damage on the boss- you actually want to minimize it, shooting him with your straight shot from a distance and milking a ton of points in the process. Things won't get too hectic until his final phase, at which point he fires more bullets. Continue avoiding bullets at the left side of the screen while putting minimal damage on the boss until he dies, and you should finish the first level at about 350,000 points.
There's nothing special for the second level. With some practice, you'll figure out where the enemies spawn and how to best handle them. The boss comes in from the left so fly over his head to get to the left of him, and you can do the same thing here. His attacks are repetitive, so just avoid them and milk him for points until he dies, which should put you over 600k. If not, you shouldn't have to play very far into level 3.https://www.twitch.tv/videos/161148355