Strategy and Tactics are best described as "Concepts on how to achieve victory". Strategy is a chosen global method of action, while tactics are short-term actions to attain specific goals.

Common Strategies

Rushing - Speed Slaughter

Porcing - If I Hold Out Long Enough, I'll Be The Last Man Standing

Map Control - Everywhere At Once

Uberweapon - Nukes, LRPCS & Superunits

Expansion - The Eradication Of Base Mentality

Planned Delaying - Just Need To Slow Them Down...

The Secret Front - Victory Through Misinformation

A Good Offense is the Best Defense - Speed, No Defense

Note On Strategies
Many of the strategies listed here are not viable in all the games which run on the Spring engine. Some have more application than others, and many may seem less than relevant to many players.

Common Tactics

Commander Bombing

Commander Kidnapping

Raiding

Swarming

Nuclear Strike

Chokepoint

Teching

Defensive Lines

Transports & Supply Lines

Dedicated Spamming

Classic Pincer

Air Domination

Squad Tactics

Artillery Creep

Ace In The Hole

Specific Supplements

NOTA Player's Guide

The basics of XTA

NOTA vs OTA Guide

Commander Tactics

Base Construction

Spring for RTS Players

Spring Replays

Tactics For Individual Mods

Resources

Theory On Strategy

Aggressive Vs. Passive Strategy

One Vs. One Tactics & Strategy

Delaying Inevitable Defeat: Development Time

Multiplayer Strategy

Strategic, Operational & Tactical Warfare

Manored's Guide about BA units

Discussions On Strategy

Lobby Client Discussion December 2005

Tactics And Hills

Airdrop Efficency

Forum Discussion January 06

Forum Discussion July 06

SomethingAwful: Spring Strategies & Tricks

Other

Spring Guide!

Individual Playing Styles

Little Tricky Tricks Video

Subjects Of Study In Relation To Strategy

Comparison Of Tactics In Different Mods

Gameplay Strategy For The Mod Developer

Gameplay Strategy For The AI Developer

Gameplay Strategy For The Map Developer

External Resources

IGN: The State of the RTS

Sun Tzu's The Art Of War

Feel free to contribute as you see fit to the Strategy and Tactics section of the Wiki as you would elsewhere, but remember to respect the work of other contributors and consult them if you seek to overhaul their contributions.