Fundamentals
1. Use Hotkeys for Production
Hotkeys allow you to perform actions much, much faster than you would otherwise be able to. By default, Unit Production Hotkeys are based on an ASDF layout on your keyboard. You can easily remember this layout and train Units by pressing the corresponding Hotkey for them, rather than clicking on their icons.
Another group of Hotkeys are "Find Unit Hotkeys" which allow you to quickly select a Unit and Building, regardless of where it is on the map. You can utilize this type of Hotkey in various situations such as when you want to find your Scout to do more Scouting, or perhaps when you want to select a Storehouse to quickly research an economy upgrade without looking for a Storehouse on the map and clicking on it.
There are many different and useful Hotkeys in the Hotkeys section of the Options menu. Take your time and learn them. You won't regret it!

2. Use Control Groups
Control groups let you select Units or Buildings that currently aren't on your screen and learning them will turn you into a much better player.
You can create a new control group by selecting a Unit or Building, holding Ctrl and then pressing a number key.
For example, Ctrl + 1 would assign control group 1 to any Unit or Building you have selected and you can simply press 1 to highlight it, wherever it is.
If you want to add new Units or Buildings to your Control group, you can select them and hold Shift + 1 to add them to your existing Control group 1.
Check the "Selection Group Hotkeys" section of the Hotkeys menu to find out more about Control Group Hotkeys.

3. Watch your Mini-map
The mini-map is an excellent tool to keep an overview of what's going on in your match. You can see enemy Units moving towards your base and prepare your defenses accordingly, always being one step ahead of your opponent.
You can also keep an eye on different Resources on the map, both for yourself and your opponent.
