Since clicking becomes quite obsolete when you get further into the game, it's best to use an autoclicker for this, set it to 20-30 clicks per second (more would lag the game for me) and leave it to run overnight.
If you object to this, using the Tapps Attacks spells autoclicks for you. The amount of clicks per second and the duration of the spell increases as you upgrade the spell, up to 20 clicks/sec for 75 seconds (1500 clicks total).