Ask Winho88 how you survive a million. I haven't even come close to that yet. I've only survived 500K twice.
Tips:
Multipliers are earned by shooting enemies. Some put it up faster than others, especially the small blue ones that come in streams. You're almost guaranteed a new multiplier from those bad boys.
Use bombs to preserve your multiplier once you get to 5x. By that, i mean don't die, and use the bombs to save yourself.
Shoot a path for your ship when things get tough.
Learn to spread your shots in an arc, to cover more area.
After that, it's just practice. I've only got over 2 million once, but i regularly score over a million.