I've seen many pro's reach up to 200, 300, and 400 APM. I'm stuck at above 100 and can't seem to break it =\

Any tips on how to get faster at SC?

I heard that some players just spam clicks, and they all add up to a high APM.

[quote author="thenonhacker" date="1203516801"]I heard that some players just spam clicks, and they all add up to a high APM.[/quote]

Yes much is just unnecessary spam.
Just watch FireBatHero :
http://youtube.com/watch?v=wyUKdXXlQ84

I know about spamming, but what about just getting faster in general? Like from 100 to 150 or so?

While some people are intentionally spamming, I had friends who have high APM but did not spam.

I think they are not using Group Hotkeys much.
Another reason why they pick a few units for microing at any moment.

Now, in Warcraft III, I've watched replays of players
doing the right-click spam thing right from the start,
I think they are doing this to warm themselves up
for the real clicks later in the game.