Download SC2 Gears. APM can be important, but eAPM is far more important. Keeping your redundancy low. Even if you're spamming, you'll be able to see where and what is spam, and how you're doing in the actual game. But SugarBear has basically hit the nail on the head -- the question you meant to ask here is how to get better at mechanics.
Think of APM as a resource, though. I'll be speaking from a Zerg perspective, but it applies to all races about equally. You have minerals, gas, supply, production (larva), and APM. You will be spending each of these resources in a variety of ways. But critical to each resource is a macro-mechanic. For the purposes of this discussion, I want to apply the concept of bottlenecking to each. Minerals/Gas -- don't forget to build stuff, and keep your production at a high level so you aren't mining more than you can output. You also can't get supply blocked, so you have to keep making overlords, otherwise again you've bottle necked yourself.
A bottle neck is just like it sounds. Look at a Pepsi bottle somewhere, and look at the neck. All of the liquid doesn't pour out at once, it's funneled through which takes longer and is much more inefficient. For a beverage, that's great, as it means we don't drown ourselves or pour soda all over our person, but in Starcraft, it means things are not coming out as smoothly as they could be. The next resource is production, which goes right back to mineral/gas -- if your production isn't high enough, your resources will show it (assuming you have perfect macro).
The final resource is the one you asked about, but it's also the most abstract so I wanted to paint a more fluid picture for you of the other resources first. APM is a resource -- you spend the APM you have/focus on what you can. But you can do things in such a manner that will reduce the load on you later. For example, imagine not using rallies off your hatcheries. All of your drones, Zerglings, overlords, and mutalisks pop out beside the hatchery, and you manually have to send them where you want them. You'll have to do this every 30-40 seconds, on top of injecting and everything else expected of you. It'd be a headache. Rally points are one way of reducing APM bottle necking.
Stephano is one of the most dedicated rally point setters I have ever seen. On his stream, you constantly see him re-rallying units mid-battle, just so they are a few steps closer when he needs them. It's really quite insane. But there are other things you can do as well, most of which is just basic control and getting used to the UI.
Shift-peeling Most people know that you can hold shift and click a unit out of a group, but they don't do much with it. Let's imagine you have a group of 16 speedlings, though, and you need to send a single ling out of that group to take the Xel'Naga tower. You can select the appropriate group (let's say it's control group 1, for our example), then right click the Xel'Naga Tower. This will send all 16 lings to the tower. Hold shift, click one of the lings on the selection panel at the bottom, then issue a new order to the group of (now) 15 lings and all of a sudden the ling is the only one going to that tower. This is incredibly beneficial as it doesn't force one to manually select individual lings. But there's a down-side here as well.
Imagine as you're taking that tower, you see a group of marines moving across the map. You have enough lings to kill this small force, so you press 1 to select your lings, and attack click into it. Great! But, you just gave up your tower, as well. For a lot of people, there's this constant fight with the towers, always having to re-send a unit, et cetera. But let's revisit the above paragraph. What happens if you add a Ctrl+1 just after shift-clicking out the single ling. Now all of a sudden your 1 key is programmed with 15 lings til you re-program it, no more fighting with the single ling at the XC tower. You never have to have units idle, sitting still any more!
Shift-rally As a Zerg player, all of my units come from eggs. So let's say I have that group of 16 lings, and I make 4 more ling eggs (8 lings total). I can rally them to a good spot on the map, and hopefully I'll remember to scoop them up eventually to add to my group. Generally, that would be done by just boxing the reinforcements and pressing shift+1 (it adds the current selection to the 1 control group), but I could also make the 4 eggs, with say 8 larva left over. So my select larva screen would have 12 larva initially, I make 4 ling eggs, so it's 4 eggs and 8 larva. I hold ctrl, click the egg -- this selects ALL eggs. I press shift+1 now, and those eggs have been added to my control group 1.
There are all kinds of tricks like this in Starcraft. But essentially, the best APM you can have is just finding a way that works for you, and saves you time. Look at where you're being inefficient, and find ways not to be.