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This achievement is not very hard. What I found useful was...
1) Stay all the way to the right most of the time
2) Shoot up/up-left most of the time
The only time I would move away from the extreme right was to grab a useful power up, usually a sheild. By shooting up/left-up, most of the enemies should die but sometimes they will come from the left, so when they do just aim a bit more to the left. None of the lasers should hit you either from the yellow aliens or the cat that spawns on the left side of the level.