Here are the opening build orders I use when I'm playing as each race.
Zerg Build Order
On your 10th drone, make an extractor and then create another drone. Then cancel the extractor, and make an overlord when you can.
14th drone, you should create a spawning pool.
15th drone, you need to make an expansion hatchery.
18th drone, make an overlord. After make 2 or 3 spine colonies at your main base to take down to the expansion hatchery after it's done. Make a queen at the expansion hatchery when you can, and make drones / overlords whenever you need.
20th drone. Make some lair upgrades and roach warren when you have 100 gas. You can pretty much go in every direction that you want to go now, as your economy will be in great shape.
Terran Build Order
In this guide you'd want to make marines from all of your barracks whenever they're available.
On your 9th SCV, make a depot. After that make your first barracks. Also you need to make some barracks at the entrance to make a "wall."
On the 13th SCV, make your second barracks. At this point you should turn your command center into an orbital command, and make another barracks with the same SCV that built this one.
14th SCV, make a depot and use this SCV to build a refinery.
16th SCV, Make your fourth barracks.
19th SCV, Make your 2nd refinery. When the 14th SCV is done building the depot then pull the last 4 SCV's and drop them on geysers. (Each refinery should have three different SCV's to it.)
At this point you can go in whatever direction you'd prefer, as you have access to anything and can really become pretty powerful.
Protoss Build Order
On your 9th probe you want to build a Pylon. After that, on your 10th you should make a gateway. Then you should chrono-boost four probes (or one boost per two probes.)
13th probe should bring you your 2nd gateway 2nd pylon. Then, as your 14th probe comes out you should create a zealot and chrono boost 2 additional probes.
16th probe should come after your 2nd gateway is finishing (or close to it,) and you should have enough resources streaming in to make more zealots and pylons.
On your 18th probe you should create two assimilators, also throw a cybernetics core in. After they're done pull 6 probes from your mines and put three of them on each geyser that you have up. Then make more probes and chrono boost whenever they're up.