Basically hold left click and don't bother even trying to time anything literally spamming is superior and no point in using any extra brain power to do anything else.

Basically the enemies will shoot or slowly go towards you. Rule of thumb, don't touch those and you usually keep living. As a bonus, you get 3 extra lives every level and you can basically tank any boss or difficult enemy and just keep spamming.

As the world record holder, my guide is extremely valid.