Protoss Tips Practice using your spell-casters: Put the AI on super easy, and hang out in the game for a little while, practicing micromanaging your Sentries, Mothership Core, High Templars and Oracles. The key to the Protoss army is that its units are weak individually, but very strong when combined with a spell caster. Use sentries to create a force field wall that prevents the enemy from retreating away from your powerful melee Zealots. Use the Mothership Core to turn your Nexus into a giant defensive canon, or create a quicksand-like field that prevents enemies from escaping, or teleport your units back to your base instantly. These abilities are the lifeblood of your army. Using them successfully can turn a one-sided loss into a tide-turning victory. Don't Neglect Chrono Boost: The best tool Protoss players have in their arsenal is the Chrono Boost ability from their Nexus. This allows them to speed up production of any unit or upgrade significantly. Use this to pump out workers at a fast rate, speedily build an early army, or to get crucial upgrades. Smart use of Chrono Boost is one of the most important skills a Protoss can learn. Unleash the SkyToss: The bread and butter of the Protoss army are the basic Gateway units like the Stalker, Sentry, and Zealot, but don't forget about your lonely Stargate. Two of the Protoss' new units are Stargate units, and the classic Void Ray has been revamped (and it's awesome.) The Tempest is a great tool for dealing with Terrans who are building a mechanical composition (heavy on mechs and tanks) since it can attack from basically halfway across the map. The Oracle is also an immensely powerful harassment tool that can decimate your opponent's economy in seconds.
Practice casting your spells
Heart of the Swarm-specific Tips Beware of Harassment: The new units that Blizzard introduced tend to be focused around harassment. With all the new tools at their disposal it's a fair bet that your enemy will try to attack your mineral line with Oracles or Mutalisks, or Reapers. Especially Terran players who now have multiple ways to eviscerate your economy. Don't assume the enemy will come right up to your front gate for a fair fight. Be prepared to defend against units that sneak into your main base. Scout, Scout, Scout: You need to know what your opponent is building so that you can build units that perform well against their army. At it's most fundamental level, SC2 is a game about information control. If you can deny your opponent information, while scouting his army/production/tech then you should be able to win easily. This was a great idea in Wings of Liberty and it's even more pronounced in Heart of the Swarm. There are more options, and the new strategies haven't been fully established yet. So there's no telling what your opponent might try. Get Detection Early: The Widow Mines of the Terran army have the potential to flat out ruin your day. If the Terran gets them into your main base they can decimate your worker line, and if you trigger a few of them with your army you can lose a lot of units instantly. There may be better strategies for dealing with Widow Mines in the future, but for now just focus on getting early detection. For Zergs that means Overseers or Spore Crawlers. For Protoss it's Observers and Photon Cannons. Terrans will need either a Missile Turret or a second Orbital Command. Use the Tutorials: Before jumping into online play try out Blizzard's many new tools for familiarizing yourself with the multiplayer portion of the game. The tutorials will give you a feel for a basic build order, and a general logic for how the race functions. Also take advantage of the new AI system which adapts itself to your play, allowing you to steadily increase your skills.
Plan to be harassed