How to increase actions per minute

Don't APM spam useless actions.

While lots of people on youtube will do this to appear better, no professional player does this. Often times jitters at the start of a match will cause them to select between multiple units but Starcraft does not register this as actions. During the course of battle you will see professional players microing units with a large number of clicks for a given move, or swap between a dozen different buildings to keep track of queues, or send new workers to mineral patches (no auto rally in SC1). This is not spam, every one of the actions has a directed purpose.

Additionally, Splitting your workers (having them divide to different patches at the beginning of a match) was necessary in Starcraft 1 as the AI was less intelligent. There have been studies in Starcraft 2 to show that the effects of this are below the margin for error. While many pro Starcraft 2 players still do this, it is hold over from Starcraft 1, not a necessary strategy.

There are a number of resources you can use to help your apm. My favorite is the SC2 Multitasking trainer map by Stet_TCL. You can find information on it here: http://www.teamliquid.net/forum/viewmessage.php?topic_id=124983

The design is to build an army to assault an enemy base while keeping a probe on an island alive through micromanagement and picking up a stranded high templar all in a time limit. It is VERY hard, but an excellent training resource.

I wouldn't worry about APM. Focus on build order, keeping your resources spent, scouting, harassing, and micro (There's already several custom maps focused on this). If you can keep all that juggled then your APM will be improving as a matter of course. Training AMP is just a way to free up your brain so you can focus on the actual strategy of the game.