How to become a 1v1 Platinium / Diamond player in 5 easy steps
1. Learn a build order that optimizes for unit production (eg, 13 gate, 13 pool).
2. Do it 100 times until you can do it blindfolded without making a mistake.
3. (Over)Saturate your mineral lines. That means 30 workers per base (24 on minerals [3 full rows of selected workers], 3 on each gas).
4. Keep your minerals and gas under 500 at all times.
5. Congratulations, you’re platinum/diamond!
Sources: some forum on the Inet :p.

Day9’s back to basics video is the bomb, but because it’s super long, here are my very own personal notes on the matter:

Strategy is having a PLAN and taking all the necessary actions to achieve that plan.
Example of a plan: having 12 stalkers asap.

Starcraft is comming up with a STRATEGY, having a plan and doing everything cleanly and on time.

MEMORY: the key to good starcraft play is not APM, mouse control or hotkey setups.
The key is to have a good memory of everything you have to do.

Never think about what you are doing right now, but about what you want to be doing after.

THE MENTAL CHECKLIST – checklist to repeat in your head constantly.
1/ Is my money low?
2/ Is my food cap getting close?
3/ Am i making probes constantly?
4/ Am i making units constantly?
5/ If i have money, what do i buy? (this is where you need to have a preset strategy)

Thought pattern very early game: supply, probe, supply probe, supply probe…
Slightly later: supply, probe, making units, keep money low, make buildings, supply, probe, making units…

Easier mental checklist to start with:
Money
Pylon
Probes

Money, pylon, probes, money, pylon, probes…

On EYE MOVEMENT:
You need to be watching the top right hand corner of the screen a lot (almost constantly).
Money’s high? Build something.
Then you need to watch the minimap the rest of the time.

So:
LOOKING AT TOP RIGHT LOOKING AT TOP RIGHT
moneys high? build something
LOOKING AT MINIMAP LOOKING AT MINIMAP

On SHORTCUTS:
Not using them is VERY BAD.

So to learn the shortcuts do this: anytime you are in a situation you do not know the shortcut, do NOT use the mouse to build the unit or building. Use the mouse to go LOOK at the shortcut, then put your mouse back in the centre of the screen AND THEN use the hotkeys to build the unit or building.

On making probes: hotkey your Nexus, (4 for example) then hit 4E4E4E repeatedly and anytime in battle etc…

On SHIFT CLICKING : a good habit is building a building with the drone, and SHIFT CLICKING a mineral patch to make sure your drone immediatly goes back to the line after completion (or warping etc).
USE SHIFT CLICKING ALL THE TIME. Shift click back all the time.
Because I did not do that in the past, I used to have SCVs hang around idle in my base next to a building that were just built.

On HOTKEYS:
What is important is to study where your Unit hotkeys are compared to your Building hotkeys.
General framework: have the stuff you click a lot on 1 to 4 and 5 to 8.
0, 9 and 8 are things you may want to have access to sometimes… but that you are not spamming all the time (upgrade buildings for ex)

Look at the 3A combination for example: it’s an easy combination for « attack move », so put a unit group in 3.
Try to put base scans on 1 for example (for terrans).

ONCE U ESTABLISHED YOUR HOTKEY LIST… USE THEM. USE THEM. USE THEM.

Remember, memory is the key. Remember the mental checklist, remember to use shortcuts, remember to use hotkeys.
The key is remembering everything to do, hence the mental checklist is top priority. Shortcuts and hotkeys will only slightly improve your game if you are great with the mental checklist.

On MOUSE CONTROL:
You can practice mouse precision by boxing at the CC, then clicking on a mineral patch. Box, click patch, box, click patch…
If you are over or undershooting it, adjust your mouse sensitivity.

Tips and tricks:
ALYWAS HAVE A QUEUD PROBE AT YOUR BASE

At the begining of the game, rally your CC to the mineral patches that are not being mined by your first 6 SCVs.

For Zergs: the mental check list is slightly different:
Keep money low
Make overlord
Make larvae
Be aware of larvae progress

When to stop manufacturing probes / SCVs etc?
Don’t think about it too much. Set yourself a mineral limit for example (750) and decide to stop making probes once you hit that.

Remembering your Mental Checklist in battle is difficult. Practice: do not micro your battles, if you loose it’s ok because for now you are trying to improve your ability to remember your checklist.