Rules 
 
1.  Only one Pro Tip per post, no copying. 
2.  Make it serious yet somewhat comical. 
3.  Do it to ease new comers into SC2, and to re-arm vets for battle. 
 
Pro Tip - Single Marines can't do shit alone, group 'em with the control + # key with a Medivac. 

pro tip 4. always build probes

Protip: If you use Grid Hotkeys, Z becomes the key to both Morph lings to Banelings, AND to make Banelings explode. Given that select zerglings and banelings makes Banelings the sub-selected unit, this can result in embarrassingly bad baneling busts.

Pro Tip - Cheese often, a win is a win.

Pro Tip- If your relaxed, your opponent has already won.

Pro tip-  Phoenix grav beam+ stalker blink= broken terran front door if they have siege tanks

You need more vespene gas

Watch your replays. Look for the points where you're not making workers, not producing units, floating too many minerals, etc. There's useful information to be gained from win and loss replays.

Remember, your opponent is probably just as scared and confused as you are. Exploit that.

Protip: Marines will be burned alive by collosi.

Protip: With enough marines, you can accomplish anything.

Protip, LEARN ORGANICALLY. If you're slaving to some youtube vids you won't be able to improvise at all and you'll be that asshole who's always rage quitting cus things didn't go exactly as planned. 
Protip 2, nobody gives a fuck that you're Diamond tier. The fact that people say it all the time should give you some clue to how prestigious and exclusive it isn't.

Pro Tip - Fail the Placements on purpose so you can figure out easier where you're supposed to be.  This causes you to be forced into copper, and let's you experiment in the League matches, and let's you try things you can't do in Custom.  Can't get lower than Copper, use it.  Also, it gets you the achievement hella easier.  >.>

Protip: Don't get absorbed by the "counter" nonsense people constantly preach. It doesn't really work that way. With some exceptions (obviously a ground-attack only unit won't be able to do well against an air unit, for example), playing well and smart will allow you to beat an army that people would say "counters" yours. I can't count the times I've destroyed Terrans who went Thors against my mutas simply by splitting my mutas well, and then laughing at the terran going "WTF OP" because he watched Husky say that Thors "hard counter" mutalisks 50 times. 
 
Don't focus on 'countering'. Focus on playing well.

Protip - Learn to rush, it's the best way to counter it.  Be prepared for rushes, until you're fully confident the other guy won't rush.  Keep the other guy on his/her toes.

You must construct additional pylons!   Actually, always keep your supply count high, getting stuck because you forgot to raise your supply cap sucks.

pro tip. The gear is in the rear! Macro management is just as important as micro. Never get tunnel vision and the minimap is your friend

" Pro Tip- If your relaxed, your opponent has already won. "

SPAWN MORE OVERLORDS

Always remember that no matter how much you know about the game people are dumb. And sometimes that dumb can beat you- I.E.-Flying a command center next to you and upgrading to plan. Fortress, Building a bunker in front of your choke, 6 Pooling, Teching up banelings, roaches, hydras and then building muts, ETC.  

Protip: Block your fucking choke.

Protip:  Void Rays are NOT OP.   1 Viking can snipe out 10 Voidrays if micro'd properly.

As a Zerg player, ALWAYS have a queen at each Hatchery spawning larva every time it's ready.  If your queens are accumulating too much energy, you are failing at zerg macro.  Preferably hotkey each hatch/queen combo to it's own control group.  Zerg macro is hell, but you need those larva.

More units don't promise a victory.  Better mirco will beat the guy massing units.

Wall your ramp against Zerg or GG. Unless you rush to a sentry or something.

If rushing marines set the barracks rally point on your group heading to the enemy base, keep pumping out to replace those who get killed