Seriously...

try drinking an energy drink or something. 
 
It should give you better reflexes and overall focus

Switch on and off between colors?

I never got good at the game but it's basically all about memorization.

play on Easy at first so the enemies don't return fire when you blow them up. Plus you can use this opportunity to concentrate on properly switching polarity. On Normal, keep in mind they will return fire with similar polarity and that when things get hairy, you shouldn't necessarily shoot everything up. The reasoning being: if the screen gets too nuts, you don't want to add more bullets to the screen yourself if you can just dodge the enemy.

I've heard that some people change the button layout so they can move more quickly. Maybe this is something you should try.

Change the button layout to something that fits you.  
 
Get used to switching polarities. 
 
Use your special attack once you've absorbed enough energy to clear the screen. It helps when there's too much on the screen. At that point, just focus on dodging and absorbing rather than shooting.
 
If you play on Normal, kill enemies of the opposite polarity so they don't fire at you upon blowing up. Easy, this doesn't happen whether you kill enemies with the same polarity or opposite.   
 
For a bigger score, master the chain system. Kill 3 enemies of the same polarity before moving to one of an opposite porarity. You can tell what your progress is by the blue/red orbs on the side of the screen. Get three to add a chain.
 
And the biggest. MEMORIZE the enemy attack patterns. If you play a level enough times, you'll know what to expect. Do whatever's necessary to remember what to do and perfect your strategy. 
 
That's all.

What I would do is watch the leaderboard replays for the top players, and just do what they do.

watch videos of top players playing.. memorize... get really good at switching polarities.