Theoretical Doctrines
Fortress Doctrine
If the enemy doesn't get a heart attack trying to plan around the defenses then there aren't enough. This is built entirely on the idea of being far too much trouble to deal with, focusing on defense to the exclusion of all else. Which, of course has the problem of being ill equipped on the assault.
Siege Doctrine
Nearly everything important, besides asteroid mining is on planet, and the occasional station. So these forces specialize in taking and holding those areas, favoring ships and equipment optimized for such operations, which tends to lead to them being at a bit of a disadvantage if caught out in the open.
Raid Doctrine
Sometimes, the best answer is to avoid pitched battles unless you stack the deck in your favor as much as possible. Something this doctrine specializes in, favoring high alpha strike power, stealth, and speed to harry armies while minimizing retribution. Though these focuses naturally means if their forces find themselves unable to disengage, they will be in big trouble
Decisive Battle Doctrine
Sometimes the best way to win is to slam into the enemy force to break them with sheer power. While not really built with much besides guns and armor, they are usually built to just pummel the enemy to oblivion without need for fancy strategies or tactics. Which, also generally leads to relatively more expensive ships that handle best in a slugging match, even though facing other fleets like a siege one in their element are not advised
Swiss Army Knife Doctrine
While this doesn't have any specialty or focus, that is a strength as much as a weakness. Helping give many options to commanders, and tools that are useful in many ways, even though they usually aren't quite as capable in any one specialty as other doctrines can be. Pretty much the Jack of all trades master of none, thanks to the lack of focus, which also allows to better fight enemies by avoiding the type of engagements they are strongest in.
Fighter Command Doctrine
This doctrine is built on heavy use of fighter-craft in the battlefield. Generally lacking in heavy-hitting anchors besides specifically-built Carrier-craft. Which is generally there more to service their attendant fighter-craft on the field. The biggest problem of the doctrine though is also it's strength, the fact the whole doctrine is built around their fighter wings, which give a quite capable force, which is lacking in areas where higher tonnage vessels fair better in.
A/N: Well, no really sure at all how applicable any of these little things I did is...